Feedback-ID: ie3de48e3:Fastmail
Date: Mon, 8 Jun 2026 18:11:02 +0200
From: =?utf-8?Q?=C3=81lvaro?= Herrera <alvherre@kurilemu.de>
To: solai v <solai.cdac@gmail.com>
Cc: Benoit =?utf-8?Q?Lobr=C3=A9au?= <benoit.lobreau@dalibo.com>,
	pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Logging parallel worker draught
Message-ID: <aiblU9GcNdd9S7sr@alvherre.pgsql>
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On 2026-Jun-08, solai v wrote:

> The patches applied cleanly, but PostgreSQL failed to build.The build
> errors indicate that log_parallel_workers,
> log_parallel_workers_options, LOG_PARALLEL_WORKERS_NONE, and
> LogParallelWorkersIfNeeded() are referenced during compilation but
> could not be found,

Yeah, I think some hunks disappeared from 0001, in the .h files as well
as the .sgml docs.  Probably just a borked merge.  I re-merged them,
here's the patchset again.  I did not review this.

-- 
Álvaro Herrera               48°01'N 7°57'E  —  https://www.EnterpriseDB.com/
"El destino baraja y nosotros jugamos" (A. Schopenhauer)

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	filename=v11-0001-Add-a-guc-for-parallel-worker-logging.patch

From b218e87a08acebf5fb5aea149b70c71c8fbd9872 Mon Sep 17 00:00:00 2001
From: benoit <benoit.lobreau@dalibo.com>
Date: Tue, 8 Oct 2024 12:39:41 +0200
Subject: [PATCH v11 1/3] Add a guc for parallel worker logging

The new guc log_parallel_workers controls whether a log message is
produced to display information on the number of workers spawned when a
parallel query or utility is executed.

The default value is `none` which disables logging. `all` displays
information for all parallel queries, whereas `shortage` displays
information only when the number of workers launched is lower than the
number of planned workers.

This new parameter can help database administrators and developers
diagnose performance issues related to parallelism and optimize the
configuration of the system accordingly.
---
 doc/src/sgml/config.sgml                      | 18 ++++++++++++++++++
 src/backend/access/transam/parallel.c         | 19 +++++++++++++++++++
 src/backend/utils/misc/guc_parameters.dat     |  8 ++++++++
 src/backend/utils/misc/guc_tables.c           |  8 ++++++++
 src/backend/utils/misc/postgresql.conf.sample |  1 +
 src/include/access/parallel.h                 | 11 +++++++++++
 src/include/utils/guc.h                       |  1 +
 7 files changed, 66 insertions(+)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index fa566c9e553..97957b34eb7 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -8404,6 +8404,24 @@ log_line_prefix = '%m [%p] %q%u@%d/%a '
       </listitem>
      </varlistentry>
 
+    <varlistentry id="guc-log-parallel-workers" xreflabel="log_parallel_workers">
+      <term><varname>log_parallel_workers</varname> (<type>enum</type>)
+      <indexterm>
+       <primary><varname>log_parallel_workers</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        Controls whether a log message about the number of workers is emitted during the
+        execution of a parallel query or utility statement. The default value is
+        <literal>none</literal> which disables logging. <literal>all</literal> emits
+        information for all parallel queries or utilities, whereas <literal>shortage</literal>
+        emits information only when the number of workers launched is lower than the number
+        of planned workers.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="guc-log-parameter-max-length" xreflabel="log_parameter_max_length">
       <term><varname>log_parameter_max_length</varname> (<type>integer</type>)
       <indexterm>
diff --git a/src/backend/access/transam/parallel.c b/src/backend/access/transam/parallel.c
index 89e9d224eec..be0531ad4bb 100644
--- a/src/backend/access/transam/parallel.c
+++ b/src/backend/access/transam/parallel.c
@@ -1671,3 +1671,22 @@ LookupParallelWorkerFunction(const char *libraryname, const char *funcname)
 	return (parallel_worker_main_type)
 		load_external_function(libraryname, funcname, true, NULL);
 }
+
+/*
+ * If required, emit information about parallel workers usage in
+ * the logs.
+ */
+void
+LogParallelWorkersIfNeeded(int log_parallel_workers,
+						   int parallel_workers_to_launch,
+						   int parallel_workers_launched)
+{
+	if ((log_parallel_workers == LOG_PARALLEL_WORKERS_ALL &&
+		 parallel_workers_to_launch > 0) ||
+		(log_parallel_workers == LOG_PARALLEL_WORKERS_SHORTAGE &&
+		 parallel_workers_to_launch != parallel_workers_launched))
+		ereport(LOG,
+				(errmsg("launched %i parallel workers (planned: %i)",
+						parallel_workers_launched,
+						parallel_workers_to_launch)));
+}
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index afaa058b046..807cee3135c 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -1786,6 +1786,14 @@
   assign_hook => 'assign_log_min_messages',
 },
 
+{ name => 'log_parallel_workers', type => 'enum', context => 'PGC_SUSET', group => 'LOGGING_WHAT',
+  short_desc => 'Log information about parallel worker usage.',
+  long_desc => '"none" doesn\'t log anything, "all" logs all parallel worker usage and "shortage" logs only when the planned workers couldn\'t be acquired',
+  variable => 'log_parallel_workers',
+  boot_val => 'LOG_PARALLEL_WORKERS_NONE',
+  options => 'log_parallel_workers_options',
+},
+
 { name => 'log_parameter_max_length', type => 'int', context => 'PGC_SUSET', group => 'LOGGING_WHAT',
   short_desc => 'Sets the maximum length in bytes of data logged for bind parameter values when logging statements.',
   long_desc => '-1 means log values in full.',
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 290ccbc543e..429a2d6e4d0 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -31,6 +31,7 @@
 
 #include "access/commit_ts.h"
 #include "access/gin.h"
+#include "access/parallel.h"
 #include "access/slru.h"
 #include "access/toast_compression.h"
 #include "access/twophase.h"
@@ -516,6 +517,12 @@ static const struct config_enum_entry data_checksums_options[] = {
 	{"off", PG_DATA_CHECKSUM_OFF, true},
 	{"inprogress-on", PG_DATA_CHECKSUM_INPROGRESS_ON, true},
 	{"inprogress-off", PG_DATA_CHECKSUM_INPROGRESS_OFF, true},
+};
+
+static const struct config_enum_entry log_parallel_workers_options[] = {
+	{"none", LOG_PARALLEL_WORKERS_NONE, false},
+	{"all", LOG_PARALLEL_WORKERS_ALL, false},
+	{"shortage", LOG_PARALLEL_WORKERS_SHORTAGE, false},
 	{NULL, 0, false}
 };
 
@@ -571,6 +578,7 @@ int			log_min_duration_statement = -1;
 int			log_parameter_max_length = -1;
 int			log_parameter_max_length_on_error = 0;
 int			log_temp_files = -1;
+int			log_parallel_workers = LOG_PARALLEL_WORKERS_NONE;
 double		log_statement_sample_rate = 1.0;
 double		log_xact_sample_rate = 0;
 char	   *backtrace_functions;
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index ac38cddaaf9..222cf6b3048 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -679,6 +679,7 @@
 #log_temp_files = -1                    # log temporary files equal or larger
                                         # than the specified size in kilobytes;
                                         # -1 disables, 0 logs all temp files
+#log_parallel_workers = none            # none, all, shortage
 #log_timezone = 'GMT'
 
 # - Process Title -
diff --git a/src/include/access/parallel.h b/src/include/access/parallel.h
index 60f857675e0..6cd42358daf 100644
--- a/src/include/access/parallel.h
+++ b/src/include/access/parallel.h
@@ -55,6 +55,13 @@ typedef struct ParallelWorkerContext
 	shm_toc    *toc;
 } ParallelWorkerContext;
 
+typedef enum
+{
+	LOG_PARALLEL_WORKERS_NONE = 0,
+	LOG_PARALLEL_WORKERS_ALL,
+	LOG_PARALLEL_WORKERS_SHORTAGE,
+}			log_parallel_workers_option_list;
+
 extern PGDLLIMPORT volatile sig_atomic_t ParallelMessagePending;
 extern PGDLLIMPORT int ParallelWorkerNumber;
 extern PGDLLIMPORT bool InitializingParallelWorker;
@@ -80,4 +87,8 @@ extern void ParallelWorkerReportLastRecEnd(XLogRecPtr last_xlog_end);
 
 extern void ParallelWorkerMain(Datum main_arg);
 
+extern void LogParallelWorkersIfNeeded(int log_parallel_workers,
+									   int parallel_workers_to_launch,
+									   int parallel_workers_launched);
+
 #endif							/* PARALLEL_H */
diff --git a/src/include/utils/guc.h b/src/include/utils/guc.h
index dc406d6651a..41d0790a9c9 100644
--- a/src/include/utils/guc.h
+++ b/src/include/utils/guc.h
@@ -303,6 +303,7 @@ extern PGDLLIMPORT int log_temp_files;
 extern PGDLLIMPORT double log_statement_sample_rate;
 extern PGDLLIMPORT double log_xact_sample_rate;
 extern PGDLLIMPORT char *backtrace_functions;
+extern PGDLLIMPORT int log_parallel_workers;
 
 extern PGDLLIMPORT int temp_file_limit;
 
-- 
2.47.3


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	filename=v11-0002-Implements-logging-for-parallel-worker-usage-in-.patch

From 309777539ec793e6efb3de8b62d41d7cb8ba0e48 Mon Sep 17 00:00:00 2001
From: benoit <benoit.lobreau@dalibo.com>
Date: Wed, 29 Jan 2025 17:10:57 +0100
Subject: [PATCH v11 2/3] Implements logging for parallel worker usage in
 utilities

This patch implements logging of parallel worker usage for:
* the index cleanup and bulkdelete phases of vacuum;
* btree, brin and gin index builds.
---
 src/backend/access/brin/brin.c        |  4 ++++
 src/backend/access/gin/gininsert.c    |  4 ++++
 src/backend/access/nbtree/nbtsort.c   |  4 ++++
 src/backend/commands/vacuumparallel.c | 13 +++++++++++++
 4 files changed, 25 insertions(+)

diff --git a/src/backend/access/brin/brin.c b/src/backend/access/brin/brin.c
index bdb30752e09..3bb04c117d8 100644
--- a/src/backend/access/brin/brin.c
+++ b/src/backend/access/brin/brin.c
@@ -2568,6 +2568,10 @@ _brin_end_parallel(BrinLeader *brinleader, BrinBuildState *state)
 	/* Shutdown worker processes */
 	WaitForParallelWorkersToFinish(brinleader->pcxt);
 
+	LogParallelWorkersIfNeeded(log_parallel_workers,
+							   brinleader->pcxt->nworkers_to_launch,
+							   brinleader->pcxt->nworkers_launched);
+
 	/*
 	 * Next, accumulate WAL usage.  (This must wait for the workers to finish,
 	 * or we might get incomplete data.)
diff --git a/src/backend/access/gin/gininsert.c b/src/backend/access/gin/gininsert.c
index cb9ed3b563c..c752cea8c60 100644
--- a/src/backend/access/gin/gininsert.c
+++ b/src/backend/access/gin/gininsert.c
@@ -1120,6 +1120,10 @@ _gin_end_parallel(GinLeader *ginleader, GinBuildState *state)
 	/* Shutdown worker processes */
 	WaitForParallelWorkersToFinish(ginleader->pcxt);
 
+	LogParallelWorkersIfNeeded(log_parallel_workers,
+							   ginleader->pcxt->nworkers_to_launch,
+							   ginleader->pcxt->nworkers_launched);
+
 	/*
 	 * Next, accumulate WAL usage.  (This must wait for the workers to finish,
 	 * or we might get incomplete data.)
diff --git a/src/backend/access/nbtree/nbtsort.c b/src/backend/access/nbtree/nbtsort.c
index 756dfa3dcf4..2670e88cd22 100644
--- a/src/backend/access/nbtree/nbtsort.c
+++ b/src/backend/access/nbtree/nbtsort.c
@@ -1615,6 +1615,10 @@ _bt_end_parallel(BTLeader *btleader)
 	/* Shutdown worker processes */
 	WaitForParallelWorkersToFinish(btleader->pcxt);
 
+	LogParallelWorkersIfNeeded(log_parallel_workers,
+							   btleader->pcxt->nworkers_to_launch,
+							   btleader->pcxt->nworkers_launched);
+
 	/*
 	 * Next, accumulate WAL usage.  (This must wait for the workers to finish,
 	 * or we might get incomplete data.)
diff --git a/src/backend/commands/vacuumparallel.c b/src/backend/commands/vacuumparallel.c
index 41cefcfde54..611d67154b9 100644
--- a/src/backend/commands/vacuumparallel.c
+++ b/src/backend/commands/vacuumparallel.c
@@ -257,6 +257,9 @@ struct ParallelVacuumState
 	int			nindexes_parallel_cleanup;
 	int			nindexes_parallel_condcleanup;
 
+	int			nworkers_to_launch;
+	int			nworkers_launched;
+
 	/* Buffer access strategy used by leader process */
 	BufferAccessStrategy bstrategy;
 
@@ -424,6 +427,9 @@ parallel_vacuum_init(Relation rel, Relation *indrels, int nindexes,
 		if ((vacoptions & VACUUM_OPTION_PARALLEL_COND_CLEANUP) != 0)
 			pvs->nindexes_parallel_condcleanup++;
 	}
+	pvs->nworkers_to_launch = 0;
+	pvs->nworkers_launched = 0;
+
 	shm_toc_insert(pcxt->toc, PARALLEL_VACUUM_KEY_INDEX_STATS, indstats);
 	pvs->indstats = indstats;
 
@@ -516,6 +522,10 @@ parallel_vacuum_end(ParallelVacuumState *pvs, IndexBulkDeleteResult **istats)
 {
 	Assert(!IsParallelWorker());
 
+	LogParallelWorkersIfNeeded(log_parallel_workers,
+							   pvs->nworkers_to_launch,
+							   pvs->nworkers_launched);
+
 	/* Copy the updated statistics */
 	for (int i = 0; i < pvs->nindexes; i++)
 	{
@@ -946,6 +956,9 @@ parallel_vacuum_process_all_indexes(ParallelVacuumState *pvs, int num_index_scan
 
 		for (int i = 0; i < pvs->pcxt->nworkers_launched; i++)
 			InstrAccumParallelQuery(&pvs->buffer_usage[i], &pvs->wal_usage[i]);
+
+		pvs->nworkers_to_launch += pvs->pcxt->nworkers_to_launch;
+		pvs->nworkers_launched += pvs->pcxt->nworkers_launched;
 	}
 
 	/*
-- 
2.47.3


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	filename=v11-0003-Implements-logging-for-parallel-worker-usage-in-.patch

From 6097a014f688be508855afe62c8cc2209e35221e Mon Sep 17 00:00:00 2001
From: benoit <benoit.lobreau@dalibo.com>
Date: Wed, 29 Jan 2025 17:15:25 +0100
Subject: [PATCH v11 3/3] Implements logging for parallel worker usage in
 queries

---
 src/backend/executor/execMain.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
index 4b30f768680..3ff7a629573 100644
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -499,6 +499,10 @@ standard_ExecutorEnd(QueryDesc *queryDesc)
 		pgstat_update_parallel_workers_stats((PgStat_Counter) estate->es_parallel_workers_to_launch,
 											 (PgStat_Counter) estate->es_parallel_workers_launched);
 
+	LogParallelWorkersIfNeeded(log_parallel_workers,
+							   estate->es_parallel_workers_to_launch,
+							   estate->es_parallel_workers_launched);
+
 	/*
 	 * Check that ExecutorFinish was called, unless in EXPLAIN-only mode. This
 	 * Assert is needed because ExecutorFinish is new as of 9.1, and callers
-- 
2.47.3


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