From: Alexander Kukushkin <cyberdemn@gmail.com>
Subject: [PATCH v9] Be more picky with WAL segment deletion in pg_rewind
Date: Sun, 6 Aug 2023 15:56:39 +0100
Make pg_rewind to be a bit wiser in terms of creating filemap:
preserve on the target all WAL segments that contain records between the
last common checkpoint and the point of divergence.
Co-authored-by: Polina Bungina <bungina@gmail.com>
---
src/bin/pg_rewind/filemap.c | 62 +++++++++++++++++-
src/bin/pg_rewind/filemap.h | 3 +
src/bin/pg_rewind/meson.build | 1 +
src/bin/pg_rewind/parsexlog.c | 24 +++++++
src/bin/pg_rewind/pg_rewind.c | 3 +
src/bin/pg_rewind/t/010_keep_recycled_wals.pl | 65 +++++++++++++++++++
6 files changed, 157 insertions(+), 1 deletion(-)
create mode 100644 src/bin/pg_rewind/t/010_keep_recycled_wals.pl
inline patch 1: src/bin/pg_rewind/filemap.c, src/bin/pg_rewind/filemap.h, src/bin/pg_rewind/meson.build and 3 more (+157/-1 lines) download inline-1.patchdiff --git a/src/bin/pg_rewind/filemap.c b/src/bin/pg_rewind/filemap.cindex 4458324c9d8..b357c28338a 100644--- a/src/bin/pg_rewind/filemap.c+++ b/src/bin/pg_rewind/filemap.c@@ -63,6 +63,28 @@ static file_entry_t *lookup_filehash_entry(const char *path);
static int final_filemap_cmp(const void *a, const void *b);
static bool check_file_excluded(const char *path, bool is_source);
+typedef struct skipwal_t+{+ const char *path;+ uint32 status;+} skipwal_t;++#define SH_PREFIX keepwalhash+#define SH_ELEMENT_TYPE skipwal_t+#define SH_KEY_TYPE const char *+#define SH_KEY path+#define SH_HASH_KEY(tb, key) hash_string(key)+#define SH_EQUAL(tb, a, b) (strcmp(a, b) == 0)+#define SH_SCOPE static inline+#define SH_RAW_ALLOCATOR pg_malloc0+#define SH_DECLARE+#define SH_DEFINE+#include "lib/simplehash.h"++static keepwalhash_hash * keepwalhash = NULL;++static bool keepwalhash_entry_exists(const char *path);+
/*
* Definition of one element part of an exclusion list, used to exclude
* contents when rewinding. "name" is the name of the file or path to
@@ -206,6 +228,35 @@ lookup_filehash_entry(const char *path)
return filehash_lookup(filehash, path);
}
+/* Initialize a hash table to store WAL file names that must be kept */+void+keepwalhash_init(void)+{+ keepwalhash = keepwalhash_create(FILEHASH_INITIAL_SIZE, NULL);+}++/* Prevent a given file deletion during rewind */+void+insert_keepwalhash_entry(const char *path)+{+ skipwal_t *entry;+ bool found;++ /* Should only be called with keepwalhash initialized */+ Assert(keepwalhash);++ entry = keepwalhash_insert(keepwalhash, path, &found);++ if (!found)+ entry->path = pg_strdup(path);+}++static bool+keepwalhash_entry_exists(const char *path)+{+ return keepwalhash_lookup(keepwalhash, path) != NULL;+}+
/*
* Callback for processing source file list.
*
@@ -685,7 +736,16 @@ decide_file_action(file_entry_t *entry)
}
else if (entry->target_exists && !entry->source_exists)
{
- /* File exists in target, but not source. Remove it. */+ /* File exists in target, but not source. */++ if (keepwalhash_entry_exists(path))+ {+ /* This is a WAL file that should be kept. */+ pg_log_debug("Not removing %s because it is required for recovery", path);+ return FILE_ACTION_NONE;+ }++ /* Otherwise remove an unexpected file. */
return FILE_ACTION_REMOVE;
}
else if (!entry->target_exists && !entry->source_exists)
diff --git a/src/bin/pg_rewind/filemap.h b/src/bin/pg_rewind/filemap.hindex 007e0f17cf4..0cb6fcae00c 100644--- a/src/bin/pg_rewind/filemap.h+++ b/src/bin/pg_rewind/filemap.h@@ -110,4 +110,7 @@ extern filemap_t *decide_file_actions(void);
extern void calculate_totals(filemap_t *filemap);
extern void print_filemap(filemap_t *filemap);
+extern void keepwalhash_init(void);+extern void insert_keepwalhash_entry(const char *path);+
#endif /* FILEMAP_H */
diff --git a/src/bin/pg_rewind/meson.build b/src/bin/pg_rewind/meson.buildindex e0f88bde221..200ebf84eb9 100644--- a/src/bin/pg_rewind/meson.build+++ b/src/bin/pg_rewind/meson.build@@ -43,6 +43,7 @@ tests += {
't/007_standby_source.pl',
't/008_min_recovery_point.pl',
't/009_growing_files.pl',
+ 't/010_keep_recycled_wals.pl',
],
},
}
diff --git a/src/bin/pg_rewind/parsexlog.c b/src/bin/pg_rewind/parsexlog.cindex 22f7351fdcd..7329c06d8fa 100644--- a/src/bin/pg_rewind/parsexlog.c+++ b/src/bin/pg_rewind/parsexlog.c@@ -176,6 +176,10 @@ findLastCheckpoint(const char *datadir, XLogRecPtr forkptr, int tliIndex,
char *errormsg;
XLogPageReadPrivate private;
+ /* Track WAL segments opened while searching a checkpoint */+ XLogSegNo segno = 0;+ TimeLineID tli = 0;+
/*
* The given fork pointer points to the end of the last common record,
* which is not necessarily the beginning of the next record, if the
@@ -217,6 +221,26 @@ findLastCheckpoint(const char *datadir, XLogRecPtr forkptr, int tliIndex,
LSN_FORMAT_ARGS(searchptr));
}
+ /* We are trying to detect if the new WAL file was opened */+ if (xlogreader->seg.ws_tli != tli || xlogreader->seg.ws_segno != segno)+ {+ char xlogfname[MAXFNAMELEN];++ tli = xlogreader->seg.ws_tli;+ segno = xlogreader->seg.ws_segno;++ snprintf(xlogfname, MAXPGPATH, XLOGDIR "/");+ XLogFileName(xlogfname + strlen(xlogfname),+ xlogreader->seg.ws_tli,+ xlogreader->seg.ws_segno, WalSegSz);++ /*+ * Make sure pg_rewind doesn't remove this file, because it is+ * required for postgres to start after rewind.+ */+ insert_keepwalhash_entry(xlogfname);+ }+
/*
* Check if it is a checkpoint record. This checkpoint record needs to
* be the latest checkpoint before WAL forked and not the checkpoint
diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.cindex 0841ab4135b..48c11417b23 100644--- a/src/bin/pg_rewind/pg_rewind.c+++ b/src/bin/pg_rewind/pg_rewind.c@@ -455,6 +455,9 @@ main(int argc, char **argv)
exit(0);
}
+ /* Hash to memorize WAL files that should be kept */+ keepwalhash_init();+
findLastCheckpoint(datadir_target, divergerec, lastcommontliIndex,
&chkptrec, &chkpttli, &chkptredo, restore_command);
pg_log_info("rewinding from last common checkpoint at %X/%X on timeline %u",
diff --git a/src/bin/pg_rewind/t/010_keep_recycled_wals.pl b/src/bin/pg_rewind/t/010_keep_recycled_wals.plnew file mode 100644index 00000000000..65caaf2faa2--- /dev/null+++ b/src/bin/pg_rewind/t/010_keep_recycled_wals.pl@@ -0,0 +1,65 @@++# Copyright (c) 2021-2024, PostgreSQL Global Development Group++#+# Test situation where a target data directory contains+# WAL files that were already recycled by the new primary.+#++use strict;+use warnings;+use PostgreSQL::Test::Utils;+use Test::More;++use FindBin;+use lib $FindBin::RealBin;++use RewindTest;++RewindTest::setup_cluster();+$node_primary->enable_archiving();+RewindTest::start_primary();++RewindTest::create_standby();+$node_standby->enable_restoring($node_primary, 0);+$node_standby->reload();++RewindTest::primary_psql("CHECKPOINT"); # last common checkpoint++# We use "perl -e 'exit(1)'" as an alternative to "false", because the last one+# might not be available on Windows, but we want to run tests cross-platform.+my $false = "$^X -e 'exit(1)'";+$node_primary->append_conf(+ 'postgresql.conf', qq(+archive_command = '$false'+));+$node_primary->reload();++# advance WAL on the primary; WAL segment will never make it to the archive+RewindTest::primary_psql("CREATE TABLE t(a int)");+RewindTest::primary_psql("INSERT INTO t VALUES(0)");+RewindTest::primary_psql("SELECT pg_switch_wal()");++RewindTest::promote_standby;++# new primary loses diverging WAL segment+RewindTest::standby_psql("INSERT INTO t values(0)");+RewindTest::standby_psql("SELECT pg_switch_wal()");++$node_standby->stop();+$node_primary->stop();++my ($stdout, $stderr) = run_command(+ [+ 'pg_rewind', '--debug',+ '--source-pgdata', $node_standby->data_dir,+ '--target-pgdata', $node_primary->data_dir,+ '--no-sync',+ ]);++like(+ $stderr,+ qr/Not removing pg_wal.* because it is required for recovery/,+ "some WAL files were skipped");++done_testing();--
2.45.2
----Next_Part(Fri_Jul_12_16_24_06_2024_549)----
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To: pgsql-bugs@postgresql.org
Cc: cyberdemn@gmail.com
Subject: Re: [PATCH v9] Be more picky with WAL segment deletion in pg_rewind
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