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[PATCH v20 1/6] Split vacuumdb to create vacuuming.c/h 196+ messages / 2 participants [nested] [flat]
* [PATCH v20 1/6] Split vacuumdb to create vacuuming.c/h @ 2025-08-30 12:39 Álvaro Herrera <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Álvaro Herrera @ 2025-08-30 12:39 UTC (permalink / raw) --- src/bin/scripts/Makefile | 4 +- src/bin/scripts/meson.build | 28 +- src/bin/scripts/vacuumdb.c | 1048 +---------------------------------- src/bin/scripts/vacuuming.c | 978 ++++++++++++++++++++++++++++++++ src/bin/scripts/vacuuming.h | 95 ++++ 5 files changed, 1119 insertions(+), 1034 deletions(-) create mode 100644 src/bin/scripts/vacuuming.c create mode 100644 src/bin/scripts/vacuuming.h diff --git a/src/bin/scripts/Makefile b/src/bin/scripts/Makefile index f6b4d40810b..019ca06455d 100644 --- a/src/bin/scripts/Makefile +++ b/src/bin/scripts/Makefile @@ -28,7 +28,7 @@ createuser: createuser.o common.o $(WIN32RES) | submake-libpq submake-libpgport dropdb: dropdb.o common.o $(WIN32RES) | submake-libpq submake-libpgport submake-libpgfeutils dropuser: dropuser.o common.o $(WIN32RES) | submake-libpq submake-libpgport submake-libpgfeutils clusterdb: clusterdb.o common.o $(WIN32RES) | submake-libpq submake-libpgport submake-libpgfeutils -vacuumdb: vacuumdb.o common.o $(WIN32RES) | submake-libpq submake-libpgport submake-libpgfeutils +vacuumdb: vacuumdb.o vacuuming.o common.o $(WIN32RES) | submake-libpq submake-libpgport submake-libpgfeutils reindexdb: reindexdb.o common.o $(WIN32RES) | submake-libpq submake-libpgport submake-libpgfeutils pg_isready: pg_isready.o common.o $(WIN32RES) | submake-libpq submake-libpgport submake-libpgfeutils @@ -50,7 +50,7 @@ uninstall: clean distclean: rm -f $(addsuffix $(X), $(PROGRAMS)) $(addsuffix .o, $(PROGRAMS)) - rm -f common.o $(WIN32RES) + rm -f common.o vacuuming.o $(WIN32RES) rm -rf tmp_check export with_icu diff --git a/src/bin/scripts/meson.build b/src/bin/scripts/meson.build index 80df7c33257..a4fed59d1c9 100644 --- a/src/bin/scripts/meson.build +++ b/src/bin/scripts/meson.build @@ -12,7 +12,6 @@ binaries = [ 'createuser', 'dropuser', 'clusterdb', - 'vacuumdb', 'reindexdb', 'pg_isready', ] @@ -35,6 +34,33 @@ foreach binary : binaries bin_targets += binary endforeach +vacuuming_common = static_library('libvacuuming_common', + files('common.c', 'vacuuming.c'), + dependencies: [frontend_code, libpq], + kwargs: internal_lib_args, +) + +binaries = [ + 'vacuumdb', +] +foreach binary : binaries + binary_sources = files('@[email protected]'.format(binary)) + + if host_system == 'windows' + binary_sources += rc_bin_gen.process(win32ver_rc, extra_args: [ + '--NAME', binary, + '--FILEDESC', '@0@ - PostgreSQL utility'.format(binary),]) + endif + + binary = executable(binary, + binary_sources, + link_with: [vacuuming_common], + dependencies: [frontend_code, libpq], + kwargs: default_bin_args, + ) + bin_targets += binary +endforeach + tests += { 'name': 'scripts', 'sd': meson.current_source_dir(), diff --git a/src/bin/scripts/vacuumdb.c b/src/bin/scripts/vacuumdb.c index fd236087e90..b1be61ddf25 100644 --- a/src/bin/scripts/vacuumdb.c +++ b/src/bin/scripts/vacuumdb.c @@ -14,92 +14,13 @@ #include <limits.h> -#include "catalog/pg_attribute_d.h" -#include "catalog/pg_class_d.h" #include "common.h" -#include "common/connect.h" #include "common/logging.h" -#include "fe_utils/cancel.h" #include "fe_utils/option_utils.h" -#include "fe_utils/parallel_slot.h" -#include "fe_utils/query_utils.h" -#include "fe_utils/simple_list.h" -#include "fe_utils/string_utils.h" - - -/* vacuum options controlled by user flags */ -typedef struct vacuumingOptions -{ - bool analyze_only; - bool verbose; - bool and_analyze; - bool full; - bool freeze; - bool disable_page_skipping; - bool skip_locked; - int min_xid_age; - int min_mxid_age; - int parallel_workers; /* >= 0 indicates user specified the - * parallel degree, otherwise -1 */ - bool no_index_cleanup; - bool force_index_cleanup; - bool do_truncate; - bool process_main; - bool process_toast; - bool skip_database_stats; - char *buffer_usage_limit; - bool missing_stats_only; -} vacuumingOptions; - -/* object filter options */ -typedef enum -{ - OBJFILTER_NONE = 0, /* no filter used */ - OBJFILTER_ALL_DBS = (1 << 0), /* -a | --all */ - OBJFILTER_DATABASE = (1 << 1), /* -d | --dbname */ - OBJFILTER_TABLE = (1 << 2), /* -t | --table */ - OBJFILTER_SCHEMA = (1 << 3), /* -n | --schema */ - OBJFILTER_SCHEMA_EXCLUDE = (1 << 4), /* -N | --exclude-schema */ -} VacObjFilter; - -static VacObjFilter objfilter = OBJFILTER_NONE; - -static SimpleStringList *retrieve_objects(PGconn *conn, - vacuumingOptions *vacopts, - SimpleStringList *objects, - bool echo); - -static void vacuum_one_database(ConnParams *cparams, - vacuumingOptions *vacopts, - int stage, - SimpleStringList *objects, - SimpleStringList **found_objs, - int concurrentCons, - const char *progname, bool echo, bool quiet); - -static void vacuum_all_databases(ConnParams *cparams, - vacuumingOptions *vacopts, - bool analyze_in_stages, - SimpleStringList *objects, - int concurrentCons, - const char *progname, bool echo, bool quiet); - -static void prepare_vacuum_command(PQExpBuffer sql, int serverVersion, - vacuumingOptions *vacopts, const char *table); - -static void run_vacuum_command(PGconn *conn, const char *sql, bool echo, - const char *table); +#include "vacuuming.h" static void help(const char *progname); - -void check_objfilter(void); - -static char *escape_quotes(const char *src); - -/* For analyze-in-stages mode */ -#define ANALYZE_NO_STAGE -1 -#define ANALYZE_NUM_STAGES 3 - +static void check_objfilter(void); int main(int argc, char *argv[]) @@ -145,10 +66,6 @@ main(int argc, char *argv[]) int c; const char *dbname = NULL; const char *maintenance_db = NULL; - char *host = NULL; - char *port = NULL; - char *username = NULL; - enum trivalue prompt_password = TRI_DEFAULT; ConnParams cparams; bool echo = false; bool quiet = false; @@ -168,13 +85,18 @@ main(int argc, char *argv[]) vacopts.process_main = true; vacopts.process_toast = true; + /* the same for connection parameters */ + memset(&cparams, 0, sizeof(cparams)); + cparams.prompt_password = TRI_DEFAULT; + pg_logging_init(argv[0]); progname = get_progname(argv[0]); set_pglocale_pgservice(argv[0], PG_TEXTDOMAIN("pgscripts")); - handle_help_version_opts(argc, argv, "vacuumdb", help); + handle_help_version_opts(argc, argv, progname, help); - while ((c = getopt_long(argc, argv, "ad:efFh:j:n:N:p:P:qt:U:vwWzZ", long_options, &optindex)) != -1) + while ((c = getopt_long(argc, argv, "ad:efFh:j:n:N:p:P:qt:U:vwWzZ", + long_options, &optindex)) != -1) { switch (c) { @@ -195,7 +117,7 @@ main(int argc, char *argv[]) vacopts.freeze = true; break; case 'h': - host = pg_strdup(optarg); + cparams.pghost = pg_strdup(optarg); break; case 'j': if (!option_parse_int(optarg, "-j/--jobs", 1, INT_MAX, @@ -211,7 +133,7 @@ main(int argc, char *argv[]) simple_string_list_append(&objects, optarg); break; case 'p': - port = pg_strdup(optarg); + cparams.pgport = pg_strdup(optarg); break; case 'P': if (!option_parse_int(optarg, "-P/--parallel", 0, INT_MAX, @@ -227,16 +149,16 @@ main(int argc, char *argv[]) tbl_count++; break; case 'U': - username = pg_strdup(optarg); + cparams.pguser = pg_strdup(optarg); break; case 'v': vacopts.verbose = true; break; case 'w': - prompt_password = TRI_NO; + cparams.prompt_password = TRI_NO; break; case 'W': - prompt_password = TRI_YES; + cparams.prompt_password = TRI_YES; break; case 'z': vacopts.and_analyze = true; @@ -380,66 +302,9 @@ main(int argc, char *argv[]) pg_fatal("cannot use the \"%s\" option without \"%s\" or \"%s\"", "missing-stats-only", "analyze-only", "analyze-in-stages"); - /* fill cparams except for dbname, which is set below */ - cparams.pghost = host; - cparams.pgport = port; - cparams.pguser = username; - cparams.prompt_password = prompt_password; - cparams.override_dbname = NULL; - - setup_cancel_handler(NULL); - - /* Avoid opening extra connections. */ - if (tbl_count && (concurrentCons > tbl_count)) - concurrentCons = tbl_count; - - if (objfilter & OBJFILTER_ALL_DBS) - { - cparams.dbname = maintenance_db; - - vacuum_all_databases(&cparams, &vacopts, - analyze_in_stages, - &objects, - concurrentCons, - progname, echo, quiet); - } - else - { - if (dbname == NULL) - { - if (getenv("PGDATABASE")) - dbname = getenv("PGDATABASE"); - else if (getenv("PGUSER")) - dbname = getenv("PGUSER"); - else - dbname = get_user_name_or_exit(progname); - } - - cparams.dbname = dbname; - - if (analyze_in_stages) - { - int stage; - SimpleStringList *found_objs = NULL; - - for (stage = 0; stage < ANALYZE_NUM_STAGES; stage++) - { - vacuum_one_database(&cparams, &vacopts, - stage, - &objects, - vacopts.missing_stats_only ? &found_objs : NULL, - concurrentCons, - progname, echo, quiet); - } - } - else - vacuum_one_database(&cparams, &vacopts, - ANALYZE_NO_STAGE, - &objects, NULL, - concurrentCons, - progname, echo, quiet); - } - + vacuuming_main(&cparams, dbname, maintenance_db, &vacopts, &objects, + analyze_in_stages, tbl_count, concurrentCons, + progname, echo, quiet); exit(0); } @@ -466,885 +331,6 @@ check_objfilter(void) pg_fatal("cannot vacuum all tables in schema(s) and exclude schema(s) at the same time"); } -/* - * Returns a newly malloc'd version of 'src' with escaped single quotes and - * backslashes. - */ -static char * -escape_quotes(const char *src) -{ - char *result = escape_single_quotes_ascii(src); - - if (!result) - pg_fatal("out of memory"); - return result; -} - -/* - * vacuum_one_database - * - * Process tables in the given database. - * - * There are two ways to specify the list of objects to process: - * - * 1) The "found_objs" parameter is a double pointer to a fully qualified list - * of objects to process, as returned by a previous call to - * vacuum_one_database(). - * - * a) If both "found_objs" (the double pointer) and "*found_objs" (the - * once-dereferenced double pointer) are not NULL, this list takes - * priority, and anything specified in "objects" is ignored. - * - * b) If "found_objs" (the double pointer) is not NULL but "*found_objs" - * (the once-dereferenced double pointer) _is_ NULL, the "objects" - * parameter takes priority, and the results of the catalog query - * described in (2) are stored in "found_objs". - * - * c) If "found_objs" (the double pointer) is NULL, the "objects" - * parameter again takes priority, and the results of the catalog query - * are not saved. - * - * 2) The "objects" parameter is a user-specified list of objects to process. - * When (1b) or (1c) applies, this function performs a catalog query to - * retrieve a fully qualified list of objects to process, as described - * below. - * - * a) If "objects" is not NULL, the catalog query gathers only the objects - * listed in "objects". - * - * b) If "objects" is NULL, all tables in the database are gathered. - * - * Note that this function is only concerned with running exactly one stage - * when in analyze-in-stages mode; caller must iterate on us if necessary. - * - * If concurrentCons is > 1, multiple connections are used to vacuum tables - * in parallel. - */ -static void -vacuum_one_database(ConnParams *cparams, - vacuumingOptions *vacopts, - int stage, - SimpleStringList *objects, - SimpleStringList **found_objs, - int concurrentCons, - const char *progname, bool echo, bool quiet) -{ - PQExpBufferData sql; - PGconn *conn; - SimpleStringListCell *cell; - ParallelSlotArray *sa; - int ntups = 0; - bool failed = false; - const char *initcmd; - SimpleStringList *ret = NULL; - const char *stage_commands[] = { - "SET default_statistics_target=1; SET vacuum_cost_delay=0;", - "SET default_statistics_target=10; RESET vacuum_cost_delay;", - "RESET default_statistics_target;" - }; - const char *stage_messages[] = { - gettext_noop("Generating minimal optimizer statistics (1 target)"), - gettext_noop("Generating medium optimizer statistics (10 targets)"), - gettext_noop("Generating default (full) optimizer statistics") - }; - - Assert(stage == ANALYZE_NO_STAGE || - (stage >= 0 && stage < ANALYZE_NUM_STAGES)); - - conn = connectDatabase(cparams, progname, echo, false, true); - - if (vacopts->disable_page_skipping && PQserverVersion(conn) < 90600) - { - PQfinish(conn); - pg_fatal("cannot use the \"%s\" option on server versions older than PostgreSQL %s", - "disable-page-skipping", "9.6"); - } - - if (vacopts->no_index_cleanup && PQserverVersion(conn) < 120000) - { - PQfinish(conn); - pg_fatal("cannot use the \"%s\" option on server versions older than PostgreSQL %s", - "no-index-cleanup", "12"); - } - - if (vacopts->force_index_cleanup && PQserverVersion(conn) < 120000) - { - PQfinish(conn); - pg_fatal("cannot use the \"%s\" option on server versions older than PostgreSQL %s", - "force-index-cleanup", "12"); - } - - if (!vacopts->do_truncate && PQserverVersion(conn) < 120000) - { - PQfinish(conn); - pg_fatal("cannot use the \"%s\" option on server versions older than PostgreSQL %s", - "no-truncate", "12"); - } - - if (!vacopts->process_main && PQserverVersion(conn) < 160000) - { - PQfinish(conn); - pg_fatal("cannot use the \"%s\" option on server versions older than PostgreSQL %s", - "no-process-main", "16"); - } - - if (!vacopts->process_toast && PQserverVersion(conn) < 140000) - { - PQfinish(conn); - pg_fatal("cannot use the \"%s\" option on server versions older than PostgreSQL %s", - "no-process-toast", "14"); - } - - if (vacopts->skip_locked && PQserverVersion(conn) < 120000) - { - PQfinish(conn); - pg_fatal("cannot use the \"%s\" option on server versions older than PostgreSQL %s", - "skip-locked", "12"); - } - - if (vacopts->min_xid_age != 0 && PQserverVersion(conn) < 90600) - { - PQfinish(conn); - pg_fatal("cannot use the \"%s\" option on server versions older than PostgreSQL %s", - "--min-xid-age", "9.6"); - } - - if (vacopts->min_mxid_age != 0 && PQserverVersion(conn) < 90600) - { - PQfinish(conn); - pg_fatal("cannot use the \"%s\" option on server versions older than PostgreSQL %s", - "--min-mxid-age", "9.6"); - } - - if (vacopts->parallel_workers >= 0 && PQserverVersion(conn) < 130000) - { - PQfinish(conn); - pg_fatal("cannot use the \"%s\" option on server versions older than PostgreSQL %s", - "--parallel", "13"); - } - - if (vacopts->buffer_usage_limit && PQserverVersion(conn) < 160000) - { - PQfinish(conn); - pg_fatal("cannot use the \"%s\" option on server versions older than PostgreSQL %s", - "--buffer-usage-limit", "16"); - } - - if (vacopts->missing_stats_only && PQserverVersion(conn) < 150000) - { - PQfinish(conn); - pg_fatal("cannot use the \"%s\" option on server versions older than PostgreSQL %s", - "--missing-stats-only", "15"); - } - - /* skip_database_stats is used automatically if server supports it */ - vacopts->skip_database_stats = (PQserverVersion(conn) >= 160000); - - if (!quiet) - { - if (stage != ANALYZE_NO_STAGE) - printf(_("%s: processing database \"%s\": %s\n"), - progname, PQdb(conn), _(stage_messages[stage])); - else - printf(_("%s: vacuuming database \"%s\"\n"), - progname, PQdb(conn)); - fflush(stdout); - } - - /* - * If the caller provided the results of a previous catalog query, just - * use that. Otherwise, run the catalog query ourselves and set the - * return variable if provided. - */ - if (found_objs && *found_objs) - ret = *found_objs; - else - { - ret = retrieve_objects(conn, vacopts, objects, echo); - if (found_objs) - *found_objs = ret; - } - - /* - * Count the number of objects in the catalog query result. If there are - * none, we are done. - */ - for (cell = ret ? ret->head : NULL; cell; cell = cell->next) - ntups++; - - if (ntups == 0) - { - PQfinish(conn); - return; - } - - /* - * Ensure concurrentCons is sane. If there are more connections than - * vacuumable relations, we don't need to use them all. - */ - if (concurrentCons > ntups) - concurrentCons = ntups; - if (concurrentCons <= 0) - concurrentCons = 1; - - /* - * All slots need to be prepared to run the appropriate analyze stage, if - * caller requested that mode. We have to prepare the initial connection - * ourselves before setting up the slots. - */ - if (stage == ANALYZE_NO_STAGE) - initcmd = NULL; - else - { - initcmd = stage_commands[stage]; - executeCommand(conn, initcmd, echo); - } - - /* - * Setup the database connections. We reuse the connection we already have - * for the first slot. If not in parallel mode, the first slot in the - * array contains the connection. - */ - sa = ParallelSlotsSetup(concurrentCons, cparams, progname, echo, initcmd); - ParallelSlotsAdoptConn(sa, conn); - - initPQExpBuffer(&sql); - - cell = ret->head; - do - { - const char *tabname = cell->val; - ParallelSlot *free_slot; - - if (CancelRequested) - { - failed = true; - goto finish; - } - - free_slot = ParallelSlotsGetIdle(sa, NULL); - if (!free_slot) - { - failed = true; - goto finish; - } - - prepare_vacuum_command(&sql, PQserverVersion(free_slot->connection), - vacopts, tabname); - - /* - * Execute the vacuum. All errors are handled in processQueryResult - * through ParallelSlotsGetIdle. - */ - ParallelSlotSetHandler(free_slot, TableCommandResultHandler, NULL); - run_vacuum_command(free_slot->connection, sql.data, - echo, tabname); - - cell = cell->next; - } while (cell != NULL); - - if (!ParallelSlotsWaitCompletion(sa)) - { - failed = true; - goto finish; - } - - /* If we used SKIP_DATABASE_STATS, mop up with ONLY_DATABASE_STATS */ - if (vacopts->skip_database_stats && stage == ANALYZE_NO_STAGE) - { - const char *cmd = "VACUUM (ONLY_DATABASE_STATS);"; - ParallelSlot *free_slot = ParallelSlotsGetIdle(sa, NULL); - - if (!free_slot) - { - failed = true; - goto finish; - } - - ParallelSlotSetHandler(free_slot, TableCommandResultHandler, NULL); - run_vacuum_command(free_slot->connection, cmd, echo, NULL); - - if (!ParallelSlotsWaitCompletion(sa)) - failed = true; - } - -finish: - ParallelSlotsTerminate(sa); - pg_free(sa); - - termPQExpBuffer(&sql); - - if (failed) - exit(1); -} - -/* - * Prepare the list of tables to process by querying the catalogs. - * - * Since we execute the constructed query with the default search_path (which - * could be unsafe), everything in this query MUST be fully qualified. - * - * First, build a WITH clause for the catalog query if any tables were - * specified, with a set of values made of relation names and their optional - * set of columns. This is used to match any provided column lists with the - * generated qualified identifiers and to filter for the tables provided via - * --table. If a listed table does not exist, the catalog query will fail. - */ -static SimpleStringList * -retrieve_objects(PGconn *conn, vacuumingOptions *vacopts, - SimpleStringList *objects, bool echo) -{ - PQExpBufferData buf; - PQExpBufferData catalog_query; - PGresult *res; - SimpleStringListCell *cell; - SimpleStringList *found_objs = palloc0(sizeof(SimpleStringList)); - bool objects_listed = false; - - initPQExpBuffer(&catalog_query); - for (cell = objects ? objects->head : NULL; cell; cell = cell->next) - { - char *just_table = NULL; - const char *just_columns = NULL; - - if (!objects_listed) - { - appendPQExpBufferStr(&catalog_query, - "WITH listed_objects (object_oid, column_list) " - "AS (\n VALUES ("); - objects_listed = true; - } - else - appendPQExpBufferStr(&catalog_query, ",\n ("); - - if (objfilter & (OBJFILTER_SCHEMA | OBJFILTER_SCHEMA_EXCLUDE)) - { - appendStringLiteralConn(&catalog_query, cell->val, conn); - appendPQExpBufferStr(&catalog_query, "::pg_catalog.regnamespace, "); - } - - if (objfilter & OBJFILTER_TABLE) - { - /* - * Split relation and column names given by the user, this is used - * to feed the CTE with values on which are performed pre-run - * validity checks as well. For now these happen only on the - * relation name. - */ - splitTableColumnsSpec(cell->val, PQclientEncoding(conn), - &just_table, &just_columns); - - appendStringLiteralConn(&catalog_query, just_table, conn); - appendPQExpBufferStr(&catalog_query, "::pg_catalog.regclass, "); - } - - if (just_columns && just_columns[0] != '\0') - appendStringLiteralConn(&catalog_query, just_columns, conn); - else - appendPQExpBufferStr(&catalog_query, "NULL"); - - appendPQExpBufferStr(&catalog_query, "::pg_catalog.text)"); - - pg_free(just_table); - } - - /* Finish formatting the CTE */ - if (objects_listed) - appendPQExpBufferStr(&catalog_query, "\n)\n"); - - appendPQExpBufferStr(&catalog_query, "SELECT c.relname, ns.nspname"); - - if (objects_listed) - appendPQExpBufferStr(&catalog_query, ", listed_objects.column_list"); - - appendPQExpBufferStr(&catalog_query, - " FROM pg_catalog.pg_class c\n" - " JOIN pg_catalog.pg_namespace ns" - " ON c.relnamespace OPERATOR(pg_catalog.=) ns.oid\n" - " CROSS JOIN LATERAL (SELECT c.relkind IN (" - CppAsString2(RELKIND_PARTITIONED_TABLE) ", " - CppAsString2(RELKIND_PARTITIONED_INDEX) ")) as p (inherited)\n" - " LEFT JOIN pg_catalog.pg_class t" - " ON c.reltoastrelid OPERATOR(pg_catalog.=) t.oid\n"); - - /* - * Used to match the tables or schemas listed by the user, completing the - * JOIN clause. - */ - if (objects_listed) - { - appendPQExpBufferStr(&catalog_query, " LEFT JOIN listed_objects" - " ON listed_objects.object_oid" - " OPERATOR(pg_catalog.=) "); - - if (objfilter & OBJFILTER_TABLE) - appendPQExpBufferStr(&catalog_query, "c.oid\n"); - else - appendPQExpBufferStr(&catalog_query, "ns.oid\n"); - } - - /* - * Exclude temporary tables, beginning the WHERE clause. - */ - appendPQExpBufferStr(&catalog_query, - " WHERE c.relpersistence OPERATOR(pg_catalog.!=) " - CppAsString2(RELPERSISTENCE_TEMP) "\n"); - - /* - * Used to match the tables or schemas listed by the user, for the WHERE - * clause. - */ - if (objects_listed) - { - if (objfilter & OBJFILTER_SCHEMA_EXCLUDE) - appendPQExpBufferStr(&catalog_query, - " AND listed_objects.object_oid IS NULL\n"); - else - appendPQExpBufferStr(&catalog_query, - " AND listed_objects.object_oid IS NOT NULL\n"); - } - - /* - * If no tables were listed, filter for the relevant relation types. If - * tables were given via --table, don't bother filtering by relation type. - * Instead, let the server decide whether a given relation can be - * processed in which case the user will know about it. - */ - if ((objfilter & OBJFILTER_TABLE) == 0) - { - /* - * vacuumdb should generally follow the behavior of the underlying - * VACUUM and ANALYZE commands. If analyze_only is true, process - * regular tables, materialized views, and partitioned tables, just - * like ANALYZE (with no specific target tables) does. Otherwise, - * process only regular tables and materialized views, since VACUUM - * skips partitioned tables when no target tables are specified. - */ - if (vacopts->analyze_only) - appendPQExpBufferStr(&catalog_query, - " AND c.relkind OPERATOR(pg_catalog.=) ANY (array[" - CppAsString2(RELKIND_RELATION) ", " - CppAsString2(RELKIND_MATVIEW) ", " - CppAsString2(RELKIND_PARTITIONED_TABLE) "])\n"); - else - appendPQExpBufferStr(&catalog_query, - " AND c.relkind OPERATOR(pg_catalog.=) ANY (array[" - CppAsString2(RELKIND_RELATION) ", " - CppAsString2(RELKIND_MATVIEW) "])\n"); - - } - - /* - * For --min-xid-age and --min-mxid-age, the age of the relation is the - * greatest of the ages of the main relation and its associated TOAST - * table. The commands generated by vacuumdb will also process the TOAST - * table for the relation if necessary, so it does not need to be - * considered separately. - */ - if (vacopts->min_xid_age != 0) - { - appendPQExpBuffer(&catalog_query, - " AND GREATEST(pg_catalog.age(c.relfrozenxid)," - " pg_catalog.age(t.relfrozenxid)) " - " OPERATOR(pg_catalog.>=) '%d'::pg_catalog.int4\n" - " AND c.relfrozenxid OPERATOR(pg_catalog.!=)" - " '0'::pg_catalog.xid\n", - vacopts->min_xid_age); - } - - if (vacopts->min_mxid_age != 0) - { - appendPQExpBuffer(&catalog_query, - " AND GREATEST(pg_catalog.mxid_age(c.relminmxid)," - " pg_catalog.mxid_age(t.relminmxid)) OPERATOR(pg_catalog.>=)" - " '%d'::pg_catalog.int4\n" - " AND c.relminmxid OPERATOR(pg_catalog.!=)" - " '0'::pg_catalog.xid\n", - vacopts->min_mxid_age); - } - - if (vacopts->missing_stats_only) - { - appendPQExpBufferStr(&catalog_query, " AND (\n"); - - /* regular stats */ - appendPQExpBufferStr(&catalog_query, - " EXISTS (SELECT NULL FROM pg_catalog.pg_attribute a\n" - " WHERE a.attrelid OPERATOR(pg_catalog.=) c.oid\n" - " AND a.attnum OPERATOR(pg_catalog.>) 0::pg_catalog.int2\n" - " AND NOT a.attisdropped\n" - " AND a.attstattarget IS DISTINCT FROM 0::pg_catalog.int2\n" - " AND a.attgenerated OPERATOR(pg_catalog.<>) " - CppAsString2(ATTRIBUTE_GENERATED_VIRTUAL) "\n" - " AND NOT EXISTS (SELECT NULL FROM pg_catalog.pg_statistic s\n" - " WHERE s.starelid OPERATOR(pg_catalog.=) a.attrelid\n" - " AND s.staattnum OPERATOR(pg_catalog.=) a.attnum\n" - " AND s.stainherit OPERATOR(pg_catalog.=) p.inherited))\n"); - - /* extended stats */ - appendPQExpBufferStr(&catalog_query, - " OR EXISTS (SELECT NULL FROM pg_catalog.pg_statistic_ext e\n" - " WHERE e.stxrelid OPERATOR(pg_catalog.=) c.oid\n" - " AND e.stxstattarget IS DISTINCT FROM 0::pg_catalog.int2\n" - " AND NOT EXISTS (SELECT NULL FROM pg_catalog.pg_statistic_ext_data d\n" - " WHERE d.stxoid OPERATOR(pg_catalog.=) e.oid\n" - " AND d.stxdinherit OPERATOR(pg_catalog.=) p.inherited))\n"); - - /* expression indexes */ - appendPQExpBufferStr(&catalog_query, - " OR EXISTS (SELECT NULL FROM pg_catalog.pg_attribute a\n" - " JOIN pg_catalog.pg_index i" - " ON i.indexrelid OPERATOR(pg_catalog.=) a.attrelid\n" - " WHERE i.indrelid OPERATOR(pg_catalog.=) c.oid\n" - " AND i.indkey[a.attnum OPERATOR(pg_catalog.-) 1::pg_catalog.int2]" - " OPERATOR(pg_catalog.=) 0::pg_catalog.int2\n" - " AND a.attnum OPERATOR(pg_catalog.>) 0::pg_catalog.int2\n" - " AND NOT a.attisdropped\n" - " AND a.attstattarget IS DISTINCT FROM 0::pg_catalog.int2\n" - " AND NOT EXISTS (SELECT NULL FROM pg_catalog.pg_statistic s\n" - " WHERE s.starelid OPERATOR(pg_catalog.=) a.attrelid\n" - " AND s.staattnum OPERATOR(pg_catalog.=) a.attnum\n" - " AND s.stainherit OPERATOR(pg_catalog.=) p.inherited))\n"); - - /* inheritance and regular stats */ - appendPQExpBufferStr(&catalog_query, - " OR EXISTS (SELECT NULL FROM pg_catalog.pg_attribute a\n" - " WHERE a.attrelid OPERATOR(pg_catalog.=) c.oid\n" - " AND a.attnum OPERATOR(pg_catalog.>) 0::pg_catalog.int2\n" - " AND NOT a.attisdropped\n" - " AND a.attstattarget IS DISTINCT FROM 0::pg_catalog.int2\n" - " AND a.attgenerated OPERATOR(pg_catalog.<>) " - CppAsString2(ATTRIBUTE_GENERATED_VIRTUAL) "\n" - " AND c.relhassubclass\n" - " AND NOT p.inherited\n" - " AND EXISTS (SELECT NULL FROM pg_catalog.pg_inherits h\n" - " WHERE h.inhparent OPERATOR(pg_catalog.=) c.oid)\n" - " AND NOT EXISTS (SELECT NULL FROM pg_catalog.pg_statistic s\n" - " WHERE s.starelid OPERATOR(pg_catalog.=) a.attrelid\n" - " AND s.staattnum OPERATOR(pg_catalog.=) a.attnum\n" - " AND s.stainherit))\n"); - - /* inheritance and extended stats */ - appendPQExpBufferStr(&catalog_query, - " OR EXISTS (SELECT NULL FROM pg_catalog.pg_statistic_ext e\n" - " WHERE e.stxrelid OPERATOR(pg_catalog.=) c.oid\n" - " AND e.stxstattarget IS DISTINCT FROM 0::pg_catalog.int2\n" - " AND c.relhassubclass\n" - " AND NOT p.inherited\n" - " AND EXISTS (SELECT NULL FROM pg_catalog.pg_inherits h\n" - " WHERE h.inhparent OPERATOR(pg_catalog.=) c.oid)\n" - " AND NOT EXISTS (SELECT NULL FROM pg_catalog.pg_statistic_ext_data d\n" - " WHERE d.stxoid OPERATOR(pg_catalog.=) e.oid\n" - " AND d.stxdinherit))\n"); - - appendPQExpBufferStr(&catalog_query, " )\n"); - } - - /* - * Execute the catalog query. We use the default search_path for this - * query for consistency with table lookups done elsewhere by the user. - */ - appendPQExpBufferStr(&catalog_query, " ORDER BY c.relpages DESC;"); - executeCommand(conn, "RESET search_path;", echo); - res = executeQuery(conn, catalog_query.data, echo); - termPQExpBuffer(&catalog_query); - PQclear(executeQuery(conn, ALWAYS_SECURE_SEARCH_PATH_SQL, echo)); - - /* - * Build qualified identifiers for each table, including the column list - * if given. - */ - initPQExpBuffer(&buf); - for (int i = 0; i < PQntuples(res); i++) - { - appendPQExpBufferStr(&buf, - fmtQualifiedIdEnc(PQgetvalue(res, i, 1), - PQgetvalue(res, i, 0), - PQclientEncoding(conn))); - - if (objects_listed && !PQgetisnull(res, i, 2)) - appendPQExpBufferStr(&buf, PQgetvalue(res, i, 2)); - - simple_string_list_append(found_objs, buf.data); - resetPQExpBuffer(&buf); - } - termPQExpBuffer(&buf); - PQclear(res); - - return found_objs; -} - -/* - * Vacuum/analyze all connectable databases. - * - * In analyze-in-stages mode, we process all databases in one stage before - * moving on to the next stage. That ensure minimal stats are available - * quickly everywhere before generating more detailed ones. - */ -static void -vacuum_all_databases(ConnParams *cparams, - vacuumingOptions *vacopts, - bool analyze_in_stages, - SimpleStringList *objects, - int concurrentCons, - const char *progname, bool echo, bool quiet) -{ - PGconn *conn; - PGresult *result; - int stage; - int i; - - conn = connectMaintenanceDatabase(cparams, progname, echo); - result = executeQuery(conn, - "SELECT datname FROM pg_database WHERE datallowconn AND datconnlimit <> -2 ORDER BY 1;", - echo); - PQfinish(conn); - - if (analyze_in_stages) - { - SimpleStringList **found_objs = NULL; - - if (vacopts->missing_stats_only) - found_objs = palloc0(PQntuples(result) * sizeof(SimpleStringList *)); - - /* - * When analyzing all databases in stages, we analyze them all in the - * fastest stage first, so that initial statistics become available - * for all of them as soon as possible. - * - * This means we establish several times as many connections, but - * that's a secondary consideration. - */ - for (stage = 0; stage < ANALYZE_NUM_STAGES; stage++) - { - for (i = 0; i < PQntuples(result); i++) - { - cparams->override_dbname = PQgetvalue(result, i, 0); - - vacuum_one_database(cparams, vacopts, - stage, - objects, - vacopts->missing_stats_only ? &found_objs[i] : NULL, - concurrentCons, - progname, echo, quiet); - } - } - } - else - { - for (i = 0; i < PQntuples(result); i++) - { - cparams->override_dbname = PQgetvalue(result, i, 0); - - vacuum_one_database(cparams, vacopts, - ANALYZE_NO_STAGE, - objects, NULL, - concurrentCons, - progname, echo, quiet); - } - } - - PQclear(result); -} - -/* - * Construct a vacuum/analyze command to run based on the given options, in the - * given string buffer, which may contain previous garbage. - * - * The table name used must be already properly quoted. The command generated - * depends on the server version involved and it is semicolon-terminated. - */ -static void -prepare_vacuum_command(PQExpBuffer sql, int serverVersion, - vacuumingOptions *vacopts, const char *table) -{ - const char *paren = " ("; - const char *comma = ", "; - const char *sep = paren; - - resetPQExpBuffer(sql); - - if (vacopts->analyze_only) - { - appendPQExpBufferStr(sql, "ANALYZE"); - - /* parenthesized grammar of ANALYZE is supported since v11 */ - if (serverVersion >= 110000) - { - if (vacopts->skip_locked) - { - /* SKIP_LOCKED is supported since v12 */ - Assert(serverVersion >= 120000); - appendPQExpBuffer(sql, "%sSKIP_LOCKED", sep); - sep = comma; - } - if (vacopts->verbose) - { - appendPQExpBuffer(sql, "%sVERBOSE", sep); - sep = comma; - } - if (vacopts->buffer_usage_limit) - { - Assert(serverVersion >= 160000); - appendPQExpBuffer(sql, "%sBUFFER_USAGE_LIMIT '%s'", sep, - vacopts->buffer_usage_limit); - sep = comma; - } - if (sep != paren) - appendPQExpBufferChar(sql, ')'); - } - else - { - if (vacopts->verbose) - appendPQExpBufferStr(sql, " VERBOSE"); - } - } - else - { - appendPQExpBufferStr(sql, "VACUUM"); - - /* parenthesized grammar of VACUUM is supported since v9.0 */ - if (serverVersion >= 90000) - { - if (vacopts->disable_page_skipping) - { - /* DISABLE_PAGE_SKIPPING is supported since v9.6 */ - Assert(serverVersion >= 90600); - appendPQExpBuffer(sql, "%sDISABLE_PAGE_SKIPPING", sep); - sep = comma; - } - if (vacopts->no_index_cleanup) - { - /* "INDEX_CLEANUP FALSE" has been supported since v12 */ - Assert(serverVersion >= 120000); - Assert(!vacopts->force_index_cleanup); - appendPQExpBuffer(sql, "%sINDEX_CLEANUP FALSE", sep); - sep = comma; - } - if (vacopts->force_index_cleanup) - { - /* "INDEX_CLEANUP TRUE" has been supported since v12 */ - Assert(serverVersion >= 120000); - Assert(!vacopts->no_index_cleanup); - appendPQExpBuffer(sql, "%sINDEX_CLEANUP TRUE", sep); - sep = comma; - } - if (!vacopts->do_truncate) - { - /* TRUNCATE is supported since v12 */ - Assert(serverVersion >= 120000); - appendPQExpBuffer(sql, "%sTRUNCATE FALSE", sep); - sep = comma; - } - if (!vacopts->process_main) - { - /* PROCESS_MAIN is supported since v16 */ - Assert(serverVersion >= 160000); - appendPQExpBuffer(sql, "%sPROCESS_MAIN FALSE", sep); - sep = comma; - } - if (!vacopts->process_toast) - { - /* PROCESS_TOAST is supported since v14 */ - Assert(serverVersion >= 140000); - appendPQExpBuffer(sql, "%sPROCESS_TOAST FALSE", sep); - sep = comma; - } - if (vacopts->skip_database_stats) - { - /* SKIP_DATABASE_STATS is supported since v16 */ - Assert(serverVersion >= 160000); - appendPQExpBuffer(sql, "%sSKIP_DATABASE_STATS", sep); - sep = comma; - } - if (vacopts->skip_locked) - { - /* SKIP_LOCKED is supported since v12 */ - Assert(serverVersion >= 120000); - appendPQExpBuffer(sql, "%sSKIP_LOCKED", sep); - sep = comma; - } - if (vacopts->full) - { - appendPQExpBuffer(sql, "%sFULL", sep); - sep = comma; - } - if (vacopts->freeze) - { - appendPQExpBuffer(sql, "%sFREEZE", sep); - sep = comma; - } - if (vacopts->verbose) - { - appendPQExpBuffer(sql, "%sVERBOSE", sep); - sep = comma; - } - if (vacopts->and_analyze) - { - appendPQExpBuffer(sql, "%sANALYZE", sep); - sep = comma; - } - if (vacopts->parallel_workers >= 0) - { - /* PARALLEL is supported since v13 */ - Assert(serverVersion >= 130000); - appendPQExpBuffer(sql, "%sPARALLEL %d", sep, - vacopts->parallel_workers); - sep = comma; - } - if (vacopts->buffer_usage_limit) - { - Assert(serverVersion >= 160000); - appendPQExpBuffer(sql, "%sBUFFER_USAGE_LIMIT '%s'", sep, - vacopts->buffer_usage_limit); - sep = comma; - } - if (sep != paren) - appendPQExpBufferChar(sql, ')'); - } - else - { - if (vacopts->full) - appendPQExpBufferStr(sql, " FULL"); - if (vacopts->freeze) - appendPQExpBufferStr(sql, " FREEZE"); - if (vacopts->verbose) - appendPQExpBufferStr(sql, " VERBOSE"); - if (vacopts->and_analyze) - appendPQExpBufferStr(sql, " ANALYZE"); - } - } - - appendPQExpBuffer(sql, " %s;", table); -} - -/* - * Send a vacuum/analyze command to the server, returning after sending the - * command. - * - * Any errors during command execution are reported to stderr. - */ -static void -run_vacuum_command(PGconn *conn, const char *sql, bool echo, - const char *table) -{ - bool status; - - if (echo) - printf("%s\n", sql); - - status = PQsendQuery(conn, sql) == 1; - - if (!status) - { - if (table) - pg_log_error("vacuuming of table \"%s\" in database \"%s\" failed: %s", - table, PQdb(conn), PQerrorMessage(conn)); - else - pg_log_error("vacuuming of database \"%s\" failed: %s", - PQdb(conn), PQerrorMessage(conn)); - } -} static void help(const char *progname) diff --git a/src/bin/scripts/vacuuming.c b/src/bin/scripts/vacuuming.c new file mode 100644 index 00000000000..9be37fcc45a --- /dev/null +++ b/src/bin/scripts/vacuuming.c @@ -0,0 +1,978 @@ +/*------------------------------------------------------------------------- + * vacuuming.c + * Common routines for vacuumdb + * + * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group + * Portions Copyright (c) 1994, Regents of the University of California + * + * src/bin/scripts/vacuuming.c + * + *------------------------------------------------------------------------- + */ + +#include "postgres_fe.h" + +#include <limits.h> + +#include "catalog/pg_attribute_d.h" +#include "catalog/pg_class_d.h" +#include "common/connect.h" +#include "common/logging.h" +#include "fe_utils/cancel.h" +#include "fe_utils/option_utils.h" +#include "fe_utils/parallel_slot.h" +#include "fe_utils/query_utils.h" +#include "fe_utils/string_utils.h" +#include "vacuuming.h" + +VacObjFilter objfilter = OBJFILTER_NONE; + + +/* + * Executes vacuum/analyze as indicated, or dies in case of failure. + */ +void +vacuuming_main(ConnParams *cparams, const char *dbname, + const char *maintenance_db, vacuumingOptions *vacopts, + SimpleStringList *objects, bool analyze_in_stages, + int tbl_count, int concurrentCons, + const char *progname, bool echo, bool quiet) +{ + setup_cancel_handler(NULL); + + /* Avoid opening extra connections. */ + if (tbl_count && (concurrentCons > tbl_count)) + concurrentCons = tbl_count; + + if (objfilter & OBJFILTER_ALL_DBS) + { + cparams->dbname = maintenance_db; + + vacuum_all_databases(cparams, vacopts, + analyze_in_stages, + objects, + concurrentCons, + progname, echo, quiet); + } + else + { + if (dbname == NULL) + { + if (getenv("PGDATABASE")) + dbname = getenv("PGDATABASE"); + else if (getenv("PGUSER")) + dbname = getenv("PGUSER"); + else + dbname = get_user_name_or_exit(progname); + } + + cparams->dbname = dbname; + + if (analyze_in_stages) + { + int stage; + SimpleStringList *found_objs = NULL; + + for (stage = 0; stage < ANALYZE_NUM_STAGES; stage++) + { + vacuum_one_database(cparams, vacopts, + stage, + objects, + vacopts->missing_stats_only ? &found_objs : NULL, + concurrentCons, + progname, echo, quiet); + } + } + else + vacuum_one_database(cparams, vacopts, + ANALYZE_NO_STAGE, + objects, NULL, + concurrentCons, + progname, echo, quiet); + } +} + + +/* + * vacuum_one_database + * + * Process tables in the given database. + * + * There are two ways to specify the list of objects to process: + * + * 1) The "found_objs" parameter is a double pointer to a fully qualified list + * of objects to process, as returned by a previous call to + * vacuum_one_database(). + * + * a) If both "found_objs" (the double pointer) and "*found_objs" (the + * once-dereferenced double pointer) are not NULL, this list takes + * priority, and anything specified in "objects" is ignored. + * + * b) If "found_objs" (the double pointer) is not NULL but "*found_objs" + * (the once-dereferenced double pointer) _is_ NULL, the "objects" + * parameter takes priority, and the results of the catalog query + * described in (2) are stored in "found_objs". + * + * c) If "found_objs" (the double pointer) is NULL, the "objects" + * parameter again takes priority, and the results of the catalog query + * are not saved. + * + * 2) The "objects" parameter is a user-specified list of objects to process. + * When (1b) or (1c) applies, this function performs a catalog query to + * retrieve a fully qualified list of objects to process, as described + * below. + * + * a) If "objects" is not NULL, the catalog query gathers only the objects + * listed in "objects". + * + * b) If "objects" is NULL, all tables in the database are gathered. + * + * Note that this function is only concerned with running exactly one stage + * when in analyze-in-stages mode; caller must iterate on us if necessary. + * + * If concurrentCons is > 1, multiple connections are used to vacuum tables + * in parallel. + */ +void +vacuum_one_database(ConnParams *cparams, + vacuumingOptions *vacopts, + int stage, + SimpleStringList *objects, + SimpleStringList **found_objs, + int concurrentCons, + const char *progname, bool echo, bool quiet) +{ + PQExpBufferData sql; + PGconn *conn; + SimpleStringListCell *cell; + ParallelSlotArray *sa; + int ntups = 0; + bool failed = false; + const char *initcmd; + SimpleStringList *ret = NULL; + const char *stage_commands[] = { + "SET default_statistics_target=1; SET vacuum_cost_delay=0;", + "SET default_statistics_target=10; RESET vacuum_cost_delay;", + "RESET default_statistics_target;" + }; + const char *stage_messages[] = { + gettext_noop("Generating minimal optimizer statistics (1 target)"), + gettext_noop("Generating medium optimizer statistics (10 targets)"), + gettext_noop("Generating default (full) optimizer statistics") + }; + + Assert(stage == ANALYZE_NO_STAGE || + (stage >= 0 && stage < ANALYZE_NUM_STAGES)); + + conn = connectDatabase(cparams, progname, echo, false, true); + + if (vacopts->disable_page_skipping && PQserverVersion(conn) < 90600) + { + PQfinish(conn); + pg_fatal("cannot use the \"%s\" option on server versions older than PostgreSQL %s", + "disable-page-skipping", "9.6"); + } + + if (vacopts->no_index_cleanup && PQserverVersion(conn) < 120000) + { + PQfinish(conn); + pg_fatal("cannot use the \"%s\" option on server versions older than PostgreSQL %s", + "no-index-cleanup", "12"); + } + + if (vacopts->force_index_cleanup && PQserverVersion(conn) < 120000) + { + PQfinish(conn); + pg_fatal("cannot use the \"%s\" option on server versions older than PostgreSQL %s", + "force-index-cleanup", "12"); + } + + if (!vacopts->do_truncate && PQserverVersion(conn) < 120000) + { + PQfinish(conn); + pg_fatal("cannot use the \"%s\" option on server versions older than PostgreSQL %s", + "no-truncate", "12"); + } + + if (!vacopts->process_main && PQserverVersion(conn) < 160000) + { + PQfinish(conn); + pg_fatal("cannot use the \"%s\" option on server versions older than PostgreSQL %s", + "no-process-main", "16"); + } + + if (!vacopts->process_toast && PQserverVersion(conn) < 140000) + { + PQfinish(conn); + pg_fatal("cannot use the \"%s\" option on server versions older than PostgreSQL %s", + "no-process-toast", "14"); + } + + if (vacopts->skip_locked && PQserverVersion(conn) < 120000) + { + PQfinish(conn); + pg_fatal("cannot use the \"%s\" option on server versions older than PostgreSQL %s", + "skip-locked", "12"); + } + + if (vacopts->min_xid_age != 0 && PQserverVersion(conn) < 90600) + { + PQfinish(conn); + pg_fatal("cannot use the \"%s\" option on server versions older than PostgreSQL %s", + "--min-xid-age", "9.6"); + } + + if (vacopts->min_mxid_age != 0 && PQserverVersion(conn) < 90600) + { + PQfinish(conn); + pg_fatal("cannot use the \"%s\" option on server versions older than PostgreSQL %s", + "--min-mxid-age", "9.6"); + } + + if (vacopts->parallel_workers >= 0 && PQserverVersion(conn) < 130000) + { + PQfinish(conn); + pg_fatal("cannot use the \"%s\" option on server versions older than PostgreSQL %s", + "--parallel", "13"); + } + + if (vacopts->buffer_usage_limit && PQserverVersion(conn) < 160000) + { + PQfinish(conn); + pg_fatal("cannot use the \"%s\" option on server versions older than PostgreSQL %s", + "--buffer-usage-limit", "16"); + } + + if (vacopts->missing_stats_only && PQserverVersion(conn) < 150000) + { + PQfinish(conn); + pg_fatal("cannot use the \"%s\" option on server versions older than PostgreSQL %s", + "--missing-stats-only", "15"); + } + + /* skip_database_stats is used automatically if server supports it */ + vacopts->skip_database_stats = (PQserverVersion(conn) >= 160000); + + if (!quiet) + { + if (stage != ANALYZE_NO_STAGE) + printf(_("%s: processing database \"%s\": %s\n"), + progname, PQdb(conn), _(stage_messages[stage])); + else + printf(_("%s: vacuuming database \"%s\"\n"), + progname, PQdb(conn)); + fflush(stdout); + } + + /* + * If the caller provided the results of a previous catalog query, just + * use that. Otherwise, run the catalog query ourselves and set the + * return variable if provided. + */ + if (found_objs && *found_objs) + ret = *found_objs; + else + { + ret = retrieve_objects(conn, vacopts, objects, echo); + if (found_objs) + *found_objs = ret; + } + + /* + * Count the number of objects in the catalog query result. If there are + * none, we are done. + */ + for (cell = ret ? ret->head : NULL; cell; cell = cell->next) + ntups++; + + if (ntups == 0) + { + PQfinish(conn); + return; + } + + /* + * Ensure concurrentCons is sane. If there are more connections than + * vacuumable relations, we don't need to use them all. + */ + if (concurrentCons > ntups) + concurrentCons = ntups; + if (concurrentCons <= 0) + concurrentCons = 1; + + /* + * All slots need to be prepared to run the appropriate analyze stage, if + * caller requested that mode. We have to prepare the initial connection + * ourselves before setting up the slots. + */ + if (stage == ANALYZE_NO_STAGE) + initcmd = NULL; + else + { + initcmd = stage_commands[stage]; + executeCommand(conn, initcmd, echo); + } + + /* + * Setup the database connections. We reuse the connection we already have + * for the first slot. If not in parallel mode, the first slot in the + * array contains the connection. + */ + sa = ParallelSlotsSetup(concurrentCons, cparams, progname, echo, initcmd); + ParallelSlotsAdoptConn(sa, conn); + + initPQExpBuffer(&sql); + + cell = ret->head; + do + { + const char *tabname = cell->val; + ParallelSlot *free_slot; + + if (CancelRequested) + { + failed = true; + goto finish; + } + + free_slot = ParallelSlotsGetIdle(sa, NULL); + if (!free_slot) + { + failed = true; + goto finish; + } + + prepare_vacuum_command(&sql, PQserverVersion(free_slot->connection), + vacopts, tabname); + + /* + * Execute the vacuum. All errors are handled in processQueryResult + * through ParallelSlotsGetIdle. + */ + ParallelSlotSetHandler(free_slot, TableCommandResultHandler, NULL); + run_vacuum_command(free_slot->connection, sql.data, + echo, tabname); + + cell = cell->next; + } while (cell != NULL); + + if (!ParallelSlotsWaitCompletion(sa)) + { + failed = true; + goto finish; + } + + /* If we used SKIP_DATABASE_STATS, mop up with ONLY_DATABASE_STATS */ + if (vacopts->skip_database_stats && + stage == ANALYZE_NO_STAGE) + { + const char *cmd = "VACUUM (ONLY_DATABASE_STATS);"; + ParallelSlot *free_slot = ParallelSlotsGetIdle(sa, NULL); + + if (!free_slot) + { + failed = true; + goto finish; + } + + ParallelSlotSetHandler(free_slot, TableCommandResultHandler, NULL); + run_vacuum_command(free_slot->connection, cmd, echo, NULL); + + if (!ParallelSlotsWaitCompletion(sa)) + failed = true; + } + +finish: + ParallelSlotsTerminate(sa); + pg_free(sa); + + termPQExpBuffer(&sql); + + if (failed) + exit(1); +} + +/* + * Prepare the list of tables to process by querying the catalogs. + * + * Since we execute the constructed query with the default search_path (which + * could be unsafe), everything in this query MUST be fully qualified. + * + * First, build a WITH clause for the catalog query if any tables were + * specified, with a set of values made of relation names and their optional + * set of columns. This is used to match any provided column lists with the + * generated qualified identifiers and to filter for the tables provided via + * --table. If a listed table does not exist, the catalog query will fail. + */ +SimpleStringList * +retrieve_objects(PGconn *conn, vacuumingOptions *vacopts, + SimpleStringList *objects, bool echo) +{ + PQExpBufferData buf; + PQExpBufferData catalog_query; + PGresult *res; + SimpleStringListCell *cell; + SimpleStringList *found_objs = palloc0(sizeof(SimpleStringList)); + bool objects_listed = false; + + initPQExpBuffer(&catalog_query); + for (cell = objects ? objects->head : NULL; cell; cell = cell->next) + { + char *just_table = NULL; + const char *just_columns = NULL; + + if (!objects_listed) + { + appendPQExpBufferStr(&catalog_query, + "WITH listed_objects (object_oid, column_list) AS (\n" + " VALUES ("); + objects_listed = true; + } + else + appendPQExpBufferStr(&catalog_query, ",\n ("); + + if (objfilter & (OBJFILTER_SCHEMA | OBJFILTER_SCHEMA_EXCLUDE)) + { + appendStringLiteralConn(&catalog_query, cell->val, conn); + appendPQExpBufferStr(&catalog_query, "::pg_catalog.regnamespace, "); + } + + if (objfilter & OBJFILTER_TABLE) + { + /* + * Split relation and column names given by the user, this is used + * to feed the CTE with values on which are performed pre-run + * validity checks as well. For now these happen only on the + * relation name. + */ + splitTableColumnsSpec(cell->val, PQclientEncoding(conn), + &just_table, &just_columns); + + appendStringLiteralConn(&catalog_query, just_table, conn); + appendPQExpBufferStr(&catalog_query, "::pg_catalog.regclass, "); + } + + if (just_columns && just_columns[0] != '\0') + appendStringLiteralConn(&catalog_query, just_columns, conn); + else + appendPQExpBufferStr(&catalog_query, "NULL"); + + appendPQExpBufferStr(&catalog_query, "::pg_catalog.text)"); + + pg_free(just_table); + } + + /* Finish formatting the CTE */ + if (objects_listed) + appendPQExpBufferStr(&catalog_query, "\n)\n"); + + appendPQExpBufferStr(&catalog_query, "SELECT c.relname, ns.nspname"); + + if (objects_listed) + appendPQExpBufferStr(&catalog_query, ", listed_objects.column_list"); + + appendPQExpBufferStr(&catalog_query, + " FROM pg_catalog.pg_class c\n" + " JOIN pg_catalog.pg_namespace ns" + " ON c.relnamespace OPERATOR(pg_catalog.=) ns.oid\n" + " CROSS JOIN LATERAL (SELECT c.relkind IN (" + CppAsString2(RELKIND_PARTITIONED_TABLE) ", " + CppAsString2(RELKIND_PARTITIONED_INDEX) ")) as p (inherited)\n" + " LEFT JOIN pg_catalog.pg_class t" + " ON c.reltoastrelid OPERATOR(pg_catalog.=) t.oid\n"); + + /* + * Used to match the tables or schemas listed by the user, completing the + * JOIN clause. + */ + if (objects_listed) + { + appendPQExpBufferStr(&catalog_query, " LEFT JOIN listed_objects" + " ON listed_objects.object_oid" + " OPERATOR(pg_catalog.=) "); + + if (objfilter & OBJFILTER_TABLE) + appendPQExpBufferStr(&catalog_query, "c.oid\n"); + else + appendPQExpBufferStr(&catalog_query, "ns.oid\n"); + } + + /* + * Exclude temporary tables, beginning the WHERE clause. + */ + appendPQExpBufferStr(&catalog_query, + " WHERE c.relpersistence OPERATOR(pg_catalog.!=) " + CppAsString2(RELPERSISTENCE_TEMP) "\n"); + + /* + * Used to match the tables or schemas listed by the user, for the WHERE + * clause. + */ + if (objects_listed) + { + if (objfilter & OBJFILTER_SCHEMA_EXCLUDE) + appendPQExpBufferStr(&catalog_query, + " AND listed_objects.object_oid IS NULL\n"); + else + appendPQExpBufferStr(&catalog_query, + " AND listed_objects.object_oid IS NOT NULL\n"); + } + + /* + * If no tables were listed, filter for the relevant relation types. If + * tables were given via --table, don't bother filtering by relation type. + * Instead, let the server decide whether a given relation can be + * processed in which case the user will know about it. + */ + if ((objfilter & OBJFILTER_TABLE) == 0) + { + /* + * vacuumdb should generally follow the behavior of the underlying + * VACUUM and ANALYZE commands. If analyze_only is true, process + * regular tables, materialized views, and partitioned tables, just + * like ANALYZE (with no specific target tables) does. Otherwise, + * process only regular tables and materialized views, since VACUUM + * skips partitioned tables when no target tables are specified. + */ + if (vacopts->analyze_only) + appendPQExpBufferStr(&catalog_query, + " AND c.relkind OPERATOR(pg_catalog.=) ANY (array[" + CppAsString2(RELKIND_RELATION) ", " + CppAsString2(RELKIND_MATVIEW) ", " + CppAsString2(RELKIND_PARTITIONED_TABLE) "])\n"); + else + appendPQExpBufferStr(&catalog_query, + " AND c.relkind OPERATOR(pg_catalog.=) ANY (array[" + CppAsString2(RELKIND_RELATION) ", " + CppAsString2(RELKIND_MATVIEW) "])\n"); + } + + /* + * For --min-xid-age and --min-mxid-age, the age of the relation is the + * greatest of the ages of the main relation and its associated TOAST + * table. The commands generated by vacuumdb will also process the TOAST + * table for the relation if necessary, so it does not need to be + * considered separately. + */ + if (vacopts->min_xid_age != 0) + { + appendPQExpBuffer(&catalog_query, + " AND GREATEST(pg_catalog.age(c.relfrozenxid)," + " pg_catalog.age(t.relfrozenxid)) " + " OPERATOR(pg_catalog.>=) '%d'::pg_catalog.int4\n" + " AND c.relfrozenxid OPERATOR(pg_catalog.!=)" + " '0'::pg_catalog.xid\n", + vacopts->min_xid_age); + } + + if (vacopts->min_mxid_age != 0) + { + appendPQExpBuffer(&catalog_query, + " AND GREATEST(pg_catalog.mxid_age(c.relminmxid)," + " pg_catalog.mxid_age(t.relminmxid)) OPERATOR(pg_catalog.>=)" + " '%d'::pg_catalog.int4\n" + " AND c.relminmxid OPERATOR(pg_catalog.!=)" + " '0'::pg_catalog.xid\n", + vacopts->min_mxid_age); + } + + if (vacopts->missing_stats_only) + { + appendPQExpBufferStr(&catalog_query, " AND (\n"); + + /* regular stats */ + appendPQExpBufferStr(&catalog_query, + " EXISTS (SELECT NULL FROM pg_catalog.pg_attribute a\n" + " WHERE a.attrelid OPERATOR(pg_catalog.=) c.oid\n" + " AND a.attnum OPERATOR(pg_catalog.>) 0::pg_catalog.int2\n" + " AND NOT a.attisdropped\n" + " AND a.attstattarget IS DISTINCT FROM 0::pg_catalog.int2\n" + " AND a.attgenerated OPERATOR(pg_catalog.<>) " + CppAsString2(ATTRIBUTE_GENERATED_VIRTUAL) "\n" + " AND NOT EXISTS (SELECT NULL FROM pg_catalog.pg_statistic s\n" + " WHERE s.starelid OPERATOR(pg_catalog.=) a.attrelid\n" + " AND s.staattnum OPERATOR(pg_catalog.=) a.attnum\n" + " AND s.stainherit OPERATOR(pg_catalog.=) p.inherited))\n"); + + /* extended stats */ + appendPQExpBufferStr(&catalog_query, + " OR EXISTS (SELECT NULL FROM pg_catalog.pg_statistic_ext e\n" + " WHERE e.stxrelid OPERATOR(pg_catalog.=) c.oid\n" + " AND e.stxstattarget IS DISTINCT FROM 0::pg_catalog.int2\n" + " AND NOT EXISTS (SELECT NULL FROM pg_catalog.pg_statistic_ext_data d\n" + " WHERE d.stxoid OPERATOR(pg_catalog.=) e.oid\n" + " AND d.stxdinherit OPERATOR(pg_catalog.=) p.inherited))\n"); + + /* expression indexes */ + appendPQExpBufferStr(&catalog_query, + " OR EXISTS (SELECT NULL FROM pg_catalog.pg_attribute a\n" + " JOIN pg_catalog.pg_index i" + " ON i.indexrelid OPERATOR(pg_catalog.=) a.attrelid\n" + " WHERE i.indrelid OPERATOR(pg_catalog.=) c.oid\n" + " AND i.indkey[a.attnum OPERATOR(pg_catalog.-) 1::pg_catalog.int2]" + " OPERATOR(pg_catalog.=) 0::pg_catalog.int2\n" + " AND a.attnum OPERATOR(pg_catalog.>) 0::pg_catalog.int2\n" + " AND NOT a.attisdropped\n" + " AND a.attstattarget IS DISTINCT FROM 0::pg_catalog.int2\n" + " AND NOT EXISTS (SELECT NULL FROM pg_catalog.pg_statistic s\n" + " WHERE s.starelid OPERATOR(pg_catalog.=) a.attrelid\n" + " AND s.staattnum OPERATOR(pg_catalog.=) a.attnum\n" + " AND s.stainherit OPERATOR(pg_catalog.=) p.inherited))\n"); + + /* inheritance and regular stats */ + appendPQExpBufferStr(&catalog_query, + " OR EXISTS (SELECT NULL FROM pg_catalog.pg_attribute a\n" + " WHERE a.attrelid OPERATOR(pg_catalog.=) c.oid\n" + " AND a.attnum OPERATOR(pg_catalog.>) 0::pg_catalog.int2\n" + " AND NOT a.attisdropped\n" + " AND a.attstattarget IS DISTINCT FROM 0::pg_catalog.int2\n" + " AND a.attgenerated OPERATOR(pg_catalog.<>) " + CppAsString2(ATTRIBUTE_GENERATED_VIRTUAL) "\n" + " AND c.relhassubclass\n" + " AND NOT p.inherited\n" + " AND EXISTS (SELECT NULL FROM pg_catalog.pg_inherits h\n" + " WHERE h.inhparent OPERATOR(pg_catalog.=) c.oid)\n" + " AND NOT EXISTS (SELECT NULL FROM pg_catalog.pg_statistic s\n" + " WHERE s.starelid OPERATOR(pg_catalog.=) a.attrelid\n" + " AND s.staattnum OPERATOR(pg_catalog.=) a.attnum\n" + " AND s.stainherit))\n"); + + /* inheritance and extended stats */ + appendPQExpBufferStr(&catalog_query, + " OR EXISTS (SELECT NULL FROM pg_catalog.pg_statistic_ext e\n" + " WHERE e.stxrelid OPERATOR(pg_catalog.=) c.oid\n" + " AND e.stxstattarget IS DISTINCT FROM 0::pg_catalog.int2\n" + " AND c.relhassubclass\n" + " AND NOT p.inherited\n" + " AND EXISTS (SELECT NULL FROM pg_catalog.pg_inherits h\n" + " WHERE h.inhparent OPERATOR(pg_catalog.=) c.oid)\n" + " AND NOT EXISTS (SELECT NULL FROM pg_catalog.pg_statistic_ext_data d\n" + " WHERE d.stxoid OPERATOR(pg_catalog.=) e.oid\n" + " AND d.stxdinherit))\n"); + + appendPQExpBufferStr(&catalog_query, " )\n"); + } + + /* + * Execute the catalog query. We use the default search_path for this + * query for consistency with table lookups done elsewhere by the user. + */ + appendPQExpBufferStr(&catalog_query, " ORDER BY c.relpages DESC;"); + executeCommand(conn, "RESET search_path;", echo); + res = executeQuery(conn, catalog_query.data, echo); + termPQExpBuffer(&catalog_query); + PQclear(executeQuery(conn, ALWAYS_SECURE_SEARCH_PATH_SQL, echo)); + + /* + * Build qualified identifiers for each table, including the column list + * if given. + */ + initPQExpBuffer(&buf); + for (int i = 0; i < PQntuples(res); i++) + { + appendPQExpBufferStr(&buf, + fmtQualifiedIdEnc(PQgetvalue(res, i, 1), + PQgetvalue(res, i, 0), + PQclientEncoding(conn))); + + if (objects_listed && !PQgetisnull(res, i, 2)) + appendPQExpBufferStr(&buf, PQgetvalue(res, i, 2)); + + simple_string_list_append(found_objs, buf.data); + resetPQExpBuffer(&buf); + } + termPQExpBuffer(&buf); + PQclear(res); + + return found_objs; +} + +/* + * Vacuum/analyze all connectable databases. + * + * In analyze-in-stages mode, we process all databases in one stage before + * moving on to the next stage. That ensure minimal stats are available + * quickly everywhere before generating more detailed ones. + */ +void +vacuum_all_databases(ConnParams *cparams, + vacuumingOptions *vacopts, + bool analyze_in_stages, + SimpleStringList *objects, + int concurrentCons, + const char *progname, bool echo, bool quiet) +{ + PGconn *conn; + PGresult *result; + int stage; + int i; + + conn = connectMaintenanceDatabase(cparams, progname, echo); + result = executeQuery(conn, + "SELECT datname FROM pg_database WHERE datallowconn AND datconnlimit <> -2 ORDER BY 1;", + echo); + PQfinish(conn); + + if (analyze_in_stages) + { + SimpleStringList **found_objs = NULL; + + if (vacopts->missing_stats_only) + found_objs = palloc0(PQntuples(result) * sizeof(SimpleStringList *)); + + /* + * When analyzing all databases in stages, we analyze them all in the + * fastest stage first, so that initial statistics become available + * for all of them as soon as possible. + * + * This means we establish several times as many connections, but + * that's a secondary consideration. + */ + for (stage = 0; stage < ANALYZE_NUM_STAGES; stage++) + { + for (i = 0; i < PQntuples(result); i++) + { + cparams->override_dbname = PQgetvalue(result, i, 0); + + vacuum_one_database(cparams, vacopts, + stage, + objects, + vacopts->missing_stats_only ? &found_objs[i] : NULL, + concurrentCons, + progname, echo, quiet); + } + } + } + else + { + for (i = 0; i < PQntuples(result); i++) + { + cparams->override_dbname = PQgetvalue(result, i, 0); + + vacuum_one_database(cparams, vacopts, + ANALYZE_NO_STAGE, + objects, NULL, + concurrentCons, + progname, echo, quiet); + } + } + + PQclear(result); +} + +/* + * Construct a vacuum/analyze command to run based on the given + * options, in the given string buffer, which may contain previous garbage. + * + * The table name used must be already properly quoted. The command generated + * depends on the server version involved and it is semicolon-terminated. + */ +void +prepare_vacuum_command(PQExpBuffer sql, int serverVersion, + vacuumingOptions *vacopts, const char *table) +{ + const char *paren = " ("; + const char *comma = ", "; + const char *sep = paren; + + resetPQExpBuffer(sql); + + if (vacopts->analyze_only) + { + appendPQExpBufferStr(sql, "ANALYZE"); + + /* parenthesized grammar of ANALYZE is supported since v11 */ + if (serverVersion >= 110000) + { + if (vacopts->skip_locked) + { + /* SKIP_LOCKED is supported since v12 */ + Assert(serverVersion >= 120000); + appendPQExpBuffer(sql, "%sSKIP_LOCKED", sep); + sep = comma; + } + if (vacopts->verbose) + { + appendPQExpBuffer(sql, "%sVERBOSE", sep); + sep = comma; + } + if (vacopts->buffer_usage_limit) + { + Assert(serverVersion >= 160000); + appendPQExpBuffer(sql, "%sBUFFER_USAGE_LIMIT '%s'", sep, + vacopts->buffer_usage_limit); + sep = comma; + } + if (sep != paren) + appendPQExpBufferChar(sql, ')'); + } + else + { + if (vacopts->verbose) + appendPQExpBufferStr(sql, " VERBOSE"); + } + } + else + { + appendPQExpBufferStr(sql, "VACUUM"); + + /* parenthesized grammar of VACUUM is supported since v9.0 */ + if (serverVersion >= 90000) + { + if (vacopts->disable_page_skipping) + { + /* DISABLE_PAGE_SKIPPING is supported since v9.6 */ + Assert(serverVersion >= 90600); + appendPQExpBuffer(sql, "%sDISABLE_PAGE_SKIPPING", sep); + sep = comma; + } + if (vacopts->no_index_cleanup) + { + /* "INDEX_CLEANUP FALSE" has been supported since v12 */ + Assert(serverVersion >= 120000); + Assert(!vacopts->force_index_cleanup); + appendPQExpBuffer(sql, "%sINDEX_CLEANUP FALSE", sep); + sep = comma; + } + if (vacopts->force_index_cleanup) + { + /* "INDEX_CLEANUP TRUE" has been supported since v12 */ + Assert(serverVersion >= 120000); + Assert(!vacopts->no_index_cleanup); + appendPQExpBuffer(sql, "%sINDEX_CLEANUP TRUE", sep); + sep = comma; + } + if (!vacopts->do_truncate) + { + /* TRUNCATE is supported since v12 */ + Assert(serverVersion >= 120000); + appendPQExpBuffer(sql, "%sTRUNCATE FALSE", sep); + sep = comma; + } + if (!vacopts->process_main) + { + /* PROCESS_MAIN is supported since v16 */ + Assert(serverVersion >= 160000); + appendPQExpBuffer(sql, "%sPROCESS_MAIN FALSE", sep); + sep = comma; + } + if (!vacopts->process_toast) + { + /* PROCESS_TOAST is supported since v14 */ + Assert(serverVersion >= 140000); + appendPQExpBuffer(sql, "%sPROCESS_TOAST FALSE", sep); + sep = comma; + } + if (vacopts->skip_database_stats) + { + /* SKIP_DATABASE_STATS is supported since v16 */ + Assert(serverVersion >= 160000); + appendPQExpBuffer(sql, "%sSKIP_DATABASE_STATS", sep); + sep = comma; + } + if (vacopts->skip_locked) + { + /* SKIP_LOCKED is supported since v12 */ + Assert(serverVersion >= 120000); + appendPQExpBuffer(sql, "%sSKIP_LOCKED", sep); + sep = comma; + } + if (vacopts->full) + { + appendPQExpBuffer(sql, "%sFULL", sep); + sep = comma; + } + if (vacopts->freeze) + { + appendPQExpBuffer(sql, "%sFREEZE", sep); + sep = comma; + } + if (vacopts->verbose) + { + appendPQExpBuffer(sql, "%sVERBOSE", sep); + sep = comma; + } + if (vacopts->and_analyze) + { + appendPQExpBuffer(sql, "%sANALYZE", sep); + sep = comma; + } + if (vacopts->parallel_workers >= 0) + { + /* PARALLEL is supported since v13 */ + Assert(serverVersion >= 130000); + appendPQExpBuffer(sql, "%sPARALLEL %d", sep, + vacopts->parallel_workers); + sep = comma; + } + if (vacopts->buffer_usage_limit) + { + Assert(serverVersion >= 160000); + appendPQExpBuffer(sql, "%sBUFFER_USAGE_LIMIT '%s'", sep, + vacopts->buffer_usage_limit); + sep = comma; + } + if (sep != paren) + appendPQExpBufferChar(sql, ')'); + } + else + { + if (vacopts->full) + appendPQExpBufferStr(sql, " FULL"); + if (vacopts->freeze) + appendPQExpBufferStr(sql, " FREEZE"); + if (vacopts->verbose) + appendPQExpBufferStr(sql, " VERBOSE"); + if (vacopts->and_analyze) + appendPQExpBufferStr(sql, " ANALYZE"); + } + } + + appendPQExpBuffer(sql, " %s;", table); +} + +/* + * Send a vacuum/analyze command to the server, returning after sending the + * command. + * + * Any errors during command execution are reported to stderr. + */ +void +run_vacuum_command(PGconn *conn, const char *sql, bool echo, + const char *table) +{ + bool status; + + if (echo) + printf("%s\n", sql); + + status = PQsendQuery(conn, sql) == 1; + + if (!status) + { + if (table) + { + pg_log_error("vacuuming of table \"%s\" in database \"%s\" failed: %s", + table, PQdb(conn), PQerrorMessage(conn)); + } + else + { + pg_log_error("vacuuming of database \"%s\" failed: %s", + PQdb(conn), PQerrorMessage(conn)); + } + } +} + +/* + * Returns a newly malloc'd version of 'src' with escaped single quotes and + * backslashes. + */ +char * +escape_quotes(const char *src) +{ + char *result = escape_single_quotes_ascii(src); + + if (!result) + pg_fatal("out of memory"); + return result; +} diff --git a/src/bin/scripts/vacuuming.h b/src/bin/scripts/vacuuming.h new file mode 100644 index 00000000000..d3f000840fa --- /dev/null +++ b/src/bin/scripts/vacuuming.h @@ -0,0 +1,95 @@ +/*------------------------------------------------------------------------- + * + * vacuuming.h + * Common declarations for vacuuming.c + * + * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group + * Portions Copyright (c) 1994, Regents of the University of California + * + * src/bin/scripts/vacuuming.h + * + *------------------------------------------------------------------------- + */ +#ifndef VACUUMING_H +#define VACUUMING_H + +#include "common.h" +#include "fe_utils/connect_utils.h" +#include "fe_utils/simple_list.h" + +/* For analyze-in-stages mode */ +#define ANALYZE_NO_STAGE -1 +#define ANALYZE_NUM_STAGES 3 + +/* vacuum options controlled by user flags */ +typedef struct vacuumingOptions +{ + bool analyze_only; + bool verbose; + bool and_analyze; + bool full; + bool freeze; + bool disable_page_skipping; + bool skip_locked; + int min_xid_age; + int min_mxid_age; + int parallel_workers; /* >= 0 indicates user specified the + * parallel degree, otherwise -1 */ + bool no_index_cleanup; + bool force_index_cleanup; + bool do_truncate; + bool process_main; + bool process_toast; + bool skip_database_stats; + char *buffer_usage_limit; + bool missing_stats_only; +} vacuumingOptions; + +/* object filter options */ +typedef enum +{ + OBJFILTER_NONE = 0, /* no filter used */ + OBJFILTER_ALL_DBS = (1 << 0), /* -a | --all */ + OBJFILTER_DATABASE = (1 << 1), /* -d | --dbname */ + OBJFILTER_TABLE = (1 << 2), /* -t | --table */ + OBJFILTER_SCHEMA = (1 << 3), /* -n | --schema */ + OBJFILTER_SCHEMA_EXCLUDE = (1 << 4), /* -N | --exclude-schema */ +} VacObjFilter; + +extern VacObjFilter objfilter; + +extern void vacuuming_main(ConnParams *cparams, const char *dbname, + const char *maintenance_db, vacuumingOptions *vacopts, + SimpleStringList *objects, bool analyze_in_stages, + int tbl_count, int concurrentCons, + const char *progname, bool echo, bool quiet); + +extern SimpleStringList *retrieve_objects(PGconn *conn, + vacuumingOptions *vacopts, + SimpleStringList *objects, + bool echo); + +extern void vacuum_one_database(ConnParams *cparams, + vacuumingOptions *vacopts, + int stage, + SimpleStringList *objects, + SimpleStringList **found_objs, + int concurrentCons, + const char *progname, bool echo, bool quiet); + +extern void vacuum_all_databases(ConnParams *cparams, + vacuumingOptions *vacopts, + bool analyze_in_stages, + SimpleStringList *objects, + int concurrentCons, + const char *progname, bool echo, bool quiet); + +extern void prepare_vacuum_command(PQExpBuffer sql, int serverVersion, + vacuumingOptions *vacopts, const char *table); + +extern void run_vacuum_command(PGconn *conn, const char *sql, bool echo, + const char *table); + +extern char *escape_quotes(const char *src); + +#endif /* VACUUMING_H */ -- 2.39.5 --3q6txozlgl6t37td Content-Type: text/x-diff; charset=utf-8 Content-Disposition: attachment; filename="v20-0002-Add-REPACK-command.patch" ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 196+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 196+ messages in thread
end of thread, other threads:[~2026-04-14 09:59 UTC | newest] Thread overview: 196+ messages (download: mbox mbox.gz follow: Atom feed) -- links below jump to the message on this page -- 2025-08-30 12:39 [PATCH v20 1/6] Split vacuumdb to create vacuuming.c/h Álvaro Herrera <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]>
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