Date: Tue, 13 Oct 2020 19:26:36 -0700
From: Noah Misch <noah@leadboat.com>
To: Peter Geoghegan <pg@bowt.ie>
Cc: Andres Freund <andres@anarazel.de>,
	Phil Florent <philflorent@hotmail.com>,
	PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Subject: Re: pgstat_report_activity() and parallel CREATE INDEX (was:
 Parallel index creation & pg_stat_activity)
Message-ID: <20201014022636.GA1962668@rfd.leadboat.com>
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On Wed, Mar 07, 2018 at 05:53:18PM -0800, Peter Geoghegan wrote:
> On Thu, Mar 1, 2018 at 2:47 PM, Peter Geoghegan <pg@bowt.ie> wrote:
> > No. Just an oversight. Looks like _bt_parallel_build_main() should
> > call pgstat_report_activity(), just like ParallelQueryMain().
> >
> > I'll come up with a patch soon.
> 
> Attached patch has parallel CREATE INDEX propagate debug_query_string
> to workers.

Two test suites segfault under the following configuration:

cat >/tmp/max_parallel.conf <<EOF
log_line_prefix = '%m [%p:%l] %q%a '
log_connections = 'true'
log_disconnections = 'true'
log_statement = 'all'
fsync = off
authentication_timeout = '600s'
wal_sender_timeout = '18000s'
wal_level = minimal
max_wal_senders = 0

# Maximize parallelism.  Many suites fail under these settings, due to plan
# changes.  That is not a bug, but new crashes do qualify as bugs.

force_parallel_mode = regress
min_parallel_index_scan_size = 0
min_parallel_table_scan_size = 0
parallel_setup_cost = 0
parallel_tuple_cost = 0
EOF
make -C src/test/modules/worker_spi check TEMP_CONFIG=/tmp/max_parallel.conf  # [1]
make -C src/test/subscription check PROVE_TESTS=t/010_truncate.pl TEMP_CONFIG=/tmp/max_parallel.conf  # [2]

In both, the crash is at the strlen(debug_query_string) from $SUBJECT.
worker_spi is easy to fix by setting debug_query_string, as attached.  Since
worker_spi has real query strings, I think that's an independent good.  In the
other suite, logical replication apply_handle_truncate() constructs an
ExecuteTruncateGuts() call without use of a query string.  Options:

1. Disable parallelism for the index build under ExecuteTruncateGuts().
   Nobody will mourn a performance loss from declining parallelism for an
   empty index, but I feel like this is fixing in the wrong place.
2. Make _bt_begin_parallel() and begin_parallel_vacuum() recognize the
   debug_query_string==NULL case and reproduce it on the worker.
3. Require bgworkers to set debug_query_string before entering code of vacuum,
   truncate, etc.  Logical replication might synthesize a DDL statement, or it
   might just use a constant string.

I tend to prefer (2), but (3) isn't bad.  Opinions?


(With debug_query_string fixed, 010_truncate.pl next fails with "cannot take
query snapshot during a parallel operation".  I'll report that separately,
probably on the thread for commit 039eb6e.)

[1]
#0  __strlen_sse2_pminub () at ../sysdeps/x86_64/multiarch/strlen-sse2-pminub.S:38
#1  0x0000000000508844 in _bt_begin_parallel (request=1, isconcurrent=<optimized out>, buildstate=0x7ffe353692a0) at nbtsort.c:1536
#2  _bt_spools_heapscan (indexInfo=0x2446768, buildstate=0x7ffe353692a0, index=..., heap=0x7ff995b85948) at nbtsort.c:394
#3  btbuild (heap=0x7ff995b85948, index=0x7ff995b85d78, indexInfo=0x2446768) at nbtsort.c:326
#4  0x0000000000568d0b in index_build (heapRelation=heapRelation@entry=0x7ff995b85948, indexRelation=indexRelation@entry=0x7ff995b85d78, indexInfo=indexInfo@entry=0x2446768, isreindex=isreindex@entry=false, 
    parallel=parallel@entry=true) at index.c:2898
#5  0x000000000056a450 in index_create (heapRelation=heapRelation@entry=0x7ff995b85948, indexRelationName=indexRelationName@entry=0x7ffe35369800 "pg_toast_16388_index", indexRelationId=16393, 
    indexRelationId@entry=0, parentIndexRelid=parentIndexRelid@entry=0, parentConstraintId=parentConstraintId@entry=0, relFileNode=relFileNode@entry=0, indexInfo=indexInfo@entry=0x2446768, 
    indexColNames=0x2445a28, accessMethodObjectId=accessMethodObjectId@entry=403, tableSpaceId=tableSpaceId@entry=0, collationObjectId=collationObjectId@entry=0x7ffe35369780, 
    classObjectId=classObjectId@entry=0x7ffe35369790, coloptions=coloptions@entry=0x7ffe35369770, reloptions=reloptions@entry=0, flags=flags@entry=1, constr_flags=constr_flags@entry=0, 
    allow_system_table_mods=allow_system_table_mods@entry=true, is_internal=is_internal@entry=true, constraintId=constraintId@entry=0x0) at index.c:1217
#6  0x000000000058ad36 in create_toast_table (rel=rel@entry=0x7ff995b7db68, toastOid=toastOid@entry=0, toastIndexOid=toastIndexOid@entry=0, reloptions=reloptions@entry=0, lockmode=lockmode@entry=8, 
    check=check@entry=false) at toasting.c:310
#7  0x000000000058afe2 in CheckAndCreateToastTable (relOid=relOid@entry=16388, reloptions=reloptions@entry=0, lockmode=lockmode@entry=8, check=check@entry=false) at toasting.c:82
#8  0x000000000058b029 in NewRelationCreateToastTable (relOid=relOid@entry=16388, reloptions=reloptions@entry=0) at toasting.c:71
#9  0x00000000007f3027 in ProcessUtilitySlow (pstate=pstate@entry=0x240dc40, pstmt=pstmt@entry=0x2409358, 
    queryString=queryString@entry=0x24056a0 "CREATE SCHEMA \"schema4\" CREATE TABLE \"counted\" (\t\ttype text CHECK (type IN ('total', 'delta')), \t\tvalue\tinteger)CREATE UNIQUE INDEX \"counted_unique_total\" ON \"counted\" (type) WHERE type = 'total'", context=context@entry=PROCESS_UTILITY_SUBCOMMAND, params=params@entry=0x0, queryEnv=queryEnv@entry=0x0, qc=qc@entry=0x0, dest=0xa91ea0 <donothingDR>)
    at utility.c:1191
#10 0x00000000007f14b4 in standard_ProcessUtility (pstmt=0x2409358, 
    queryString=0x24056a0 "CREATE SCHEMA \"schema4\" CREATE TABLE \"counted\" (\t\ttype text CHECK (type IN ('total', 'delta')), \t\tvalue\tinteger)CREATE UNIQUE INDEX \"counted_unique_total\" ON \"counted\" (type) WHERE type = 'total'", context=PROCESS_UTILITY_SUBCOMMAND, params=0x0, queryEnv=0x0, dest=0xa91ea0 <donothingDR>, qc=0x0) at utility.c:1071
#11 0x0000000000615ba6 in CreateSchemaCommand (stmt=stmt@entry=0x2408b40, 
    queryString=queryString@entry=0x24056a0 "CREATE SCHEMA \"schema4\" CREATE TABLE \"counted\" (\t\ttype text CHECK (type IN ('total', 'delta')), \t\tvalue\tinteger)CREATE UNIQUE INDEX \"counted_unique_total\" ON \"counted\" (type) WHERE type = 'total'", stmt_location=0, stmt_len=0) at schemacmds.c:192
#12 0x00000000007f2365 in ProcessUtilitySlow (pstate=pstate@entry=0x24090d0, pstmt=pstmt@entry=0x2408d98, 
    queryString=queryString@entry=0x24056a0 "CREATE SCHEMA \"schema4\" CREATE TABLE \"counted\" (\t\ttype text CHECK (type IN ('total', 'delta')), \t\tvalue\tinteger)CREATE UNIQUE INDEX \"counted_unique_total\" ON \"counted\" (type) WHERE type = 'total'", context=context@entry=PROCESS_UTILITY_QUERY, params=params@entry=0x0, queryEnv=queryEnv@entry=0x0, qc=qc@entry=0x7ffe35369fd0, dest=0xa91de0 <spi_printtupDR>)
    at utility.c:1125
#13 0x00000000007f14b4 in standard_ProcessUtility (pstmt=0x2408d98, 
    queryString=0x24056a0 "CREATE SCHEMA \"schema4\" CREATE TABLE \"counted\" (\t\ttype text CHECK (type IN ('total', 'delta')), \t\tvalue\tinteger)CREATE UNIQUE INDEX \"counted_unique_total\" ON \"counted\" (type) WHERE type = 'total'", context=PROCESS_UTILITY_QUERY, params=0x0, queryEnv=0x0, dest=0xa91de0 <spi_printtupDR>, qc=0x7ffe35369fd0) at utility.c:1071
#14 0x00000000006a1ace in _SPI_execute_plan (plan=plan@entry=0x7ffe3536a050, paramLI=paramLI@entry=0x0, snapshot=snapshot@entry=0x0, crosscheck_snapshot=crosscheck_snapshot@entry=0x0, 
    read_only=read_only@entry=false, fire_triggers=fire_triggers@entry=true, tcount=tcount@entry=0, caller_dest=caller_dest@entry=0x0) at spi.c:2443
#15 0x00000000006a2102 in SPI_execute (
    src=0x24056a0 "CREATE SCHEMA \"schema4\" CREATE TABLE \"counted\" (\t\ttype text CHECK (type IN ('total', 'delta')), \t\tvalue\tinteger)CREATE UNIQUE INDEX \"counted_unique_total\" ON \"counted\" (type) WHERE type = 'total'", read_only=read_only@entry=false, tcount=tcount@entry=0) at spi.c:515
#16 0x00007ff98a80592f in initialize_worker_spi (table=0x237d268) at worker_spi.c:150
#17 worker_spi_main (main_arg=<optimized out>) at worker_spi.c:187
#18 0x0000000000753f0f in StartBackgroundWorker () at bgworker.c:820

[2]
#0  __strlen_sse2_pminub () at ../sysdeps/x86_64/multiarch/strlen-sse2-pminub.S:38
#1  0x0000000000508844 in _bt_begin_parallel (request=1, isconcurrent=<optimized out>, buildstate=0x7ffdc868f310) at nbtsort.c:1536
#2  _bt_spools_heapscan (indexInfo=0x1c5bb48, buildstate=0x7ffdc868f310, index=..., heap=0x7f7f33bad800) at nbtsort.c:394
#3  btbuild (heap=0x7f7f33bad800, index=0x7f7f33badd98, indexInfo=0x1c5bb48) at nbtsort.c:326
#4  0x0000000000568d0b in index_build (heapRelation=heapRelation@entry=0x7f7f33bad800, indexRelation=indexRelation@entry=0x7f7f33badd98, indexInfo=indexInfo@entry=0x1c5bb48, isreindex=isreindex@entry=true, 
    parallel=parallel@entry=true) at index.c:2898
#5  0x000000000056baea in reindex_index (indexId=indexId@entry=16387, skip_constraint_checks=<optimized out>, persistence=persistence@entry=112 'p', options=options@entry=0) at index.c:3541
#6  0x000000000056c060 in reindex_relation (relid=<optimized out>, flags=flags@entry=1, options=options@entry=0) at index.c:3764
#7  0x000000000062e5a7 in ExecuteTruncateGuts (explicit_rels=explicit_rels@entry=0x1c5ae60, relids=<optimized out>, relids_logged=relids_logged@entry=0x1c5bd50, behavior=behavior@entry=DROP_RESTRICT, 
    restart_seqs=<optimized out>) at tablecmds.c:1890
#8  0x000000000078c099 in apply_handle_truncate (s=0x7ffdc868f7b0) at worker.c:1879
#9  apply_dispatch (s=s@entry=0x7ffdc868f890) at worker.c:1930
#10 0x000000000078cfbb in LogicalRepApplyLoop (last_received=23166784) at worker.c:2155
#11 ApplyWorkerMain (main_arg=<optimized out>) at worker.c:3101
#12 0x0000000000753f0f in StartBackgroundWorker () at bgworker.c:820
#13 0x000000000076162d in do_start_bgworker (rw=0x1bdbb50) at postmaster.c:5890
#14 maybe_start_bgworkers () at postmaster.c:6115
#15 0x00000000007621ae in sigusr1_handler (postgres_signal_arg=<optimized out>) at postmaster.c:5276
#16 <signal handler called>
#17 0x00007f7f31f1d983 in __select_nocancel () at ../sysdeps/unix/syscall-template.S:81
#18 0x00000000004881cf in ServerLoop () at postmaster.c:1706
#19 0x0000000000763885 in PostmasterMain (argc=argc@entry=4, argv=argv@entry=0x1bb3030) at postmaster.c:1415
#20 0x000000000048a56d in main (argc=4, argv=0x1bb3030) at main.c:209

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commit 753a321
Author:     Noah Misch <noah@leadboat.com>
AuthorDate: Tue Oct 13 17:01:40 2020 -0700
Commit:     Noah Misch <noah@leadboat.com>
CommitDate: Tue Oct 13 17:01:40 2020 -0700

    worker_spi: set debug_query_string for each SPI_execute
---
 src/test/modules/worker_spi/worker_spi.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/test/modules/worker_spi/worker_spi.c b/src/test/modules/worker_spi/worker_spi.c
index 1c7b17c..daf6c1d 100644
--- a/src/test/modules/worker_spi/worker_spi.c
+++ b/src/test/modules/worker_spi/worker_spi.c
@@ -113,16 +113,17 @@ initialize_worker_spi(worktable *table)
 	SPI_connect();
 	PushActiveSnapshot(GetTransactionSnapshot());
 	pgstat_report_activity(STATE_RUNNING, "initializing worker_spi schema");
 
 	/* XXX could we use CREATE SCHEMA IF NOT EXISTS? */
 	initStringInfo(&buf);
 	appendStringInfo(&buf, "select count(*) from pg_namespace where nspname = '%s'",
 					 table->schema);
+	debug_query_string = buf.data;
 
 	ret = SPI_execute(buf.data, true, 0);
 	if (ret != SPI_OK_SELECT)
 		elog(FATAL, "SPI_execute failed: error code %d", ret);
 
 	if (SPI_processed != 1)
 		elog(FATAL, "not a singleton result");
 
@@ -138,30 +139,32 @@ initialize_worker_spi(worktable *table)
 		appendStringInfo(&buf,
 						 "CREATE SCHEMA \"%s\" "
 						 "CREATE TABLE \"%s\" ("
 						 "		type text CHECK (type IN ('total', 'delta')), "
 						 "		value	integer)"
 						 "CREATE UNIQUE INDEX \"%s_unique_total\" ON \"%s\" (type) "
 						 "WHERE type = 'total'",
 						 table->schema, table->name, table->name, table->name);
+		debug_query_string = buf.data;
 
 		/* set statement start time */
 		SetCurrentStatementStartTimestamp();
 
 		ret = SPI_execute(buf.data, false, 0);
 
 		if (ret != SPI_OK_UTILITY)
 			elog(FATAL, "failed to create my schema");
 	}
 
 	SPI_finish();
 	PopActiveSnapshot();
 	CommitTransactionCommand();
 	pgstat_report_activity(STATE_IDLE, NULL);
+	debug_query_string = NULL;
 }
 
 void
 worker_spi_main(Datum main_arg)
 {
 	int			index = DatumGetInt32(main_arg);
 	worktable  *table;
 	StringInfoData buf;
@@ -206,16 +209,17 @@ worker_spi_main(Datum main_arg)
 					 "UPDATE %s.%s "
 					 "SET value = %s.value + total.sum "
 					 "FROM total WHERE type = 'total' "
 					 "RETURNING %s.value",
 					 table->schema, table->name,
 					 table->schema, table->name,
 					 table->name,
 					 table->name);
+	debug_query_string = buf.data;
 
 	/*
 	 * Main loop: do this until the SIGTERM handler tells us to terminate
 	 */
 	while (!got_sigterm)
 	{
 		int			ret;
 

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