V7_0001-Add-a-guc-for-parallel-worker-logging.patch

From 5ae1a4e619c1d7c8e899641e16dda831e792438d Mon Sep 17 00:00:00 2001
From: benoit <benoit.lobreau@dalibo.com>
Date: Tue, 8 Oct 2024 12:39:41 +0200
Subject: [PATCH 1/4] 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         | 18 ++++++++++++++++++
 src/backend/utils/misc/guc_tables.c           | 12 ++++++++++++
 src/backend/utils/misc/postgresql.conf.sample |  1 +
 src/include/access/parallel.h                 | 19 +++++++++++++++++++
 5 files changed, 68 insertions(+)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index a782f109982..f8c879f1c10 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -7612,6 +7612,24 @@ 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 7817bedc2ef..d18d203d178 100644
--- a/src/backend/access/transam/parallel.c
+++ b/src/backend/access/transam/parallel.c
@@ -1659,3 +1659,21 @@ LookupParallelWorkerFunction(const char *libraryname, const char *funcname)
 	return (parallel_worker_main_type)
 		load_external_function(libraryname, funcname, true, NULL);
 }
+
+/*
+ * This function emits information about workers in the logs depending
+ * on the setting of log_parallel_workers
+ */
+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))
+		elog(LOG, "launched %i parallel workers (planned: %i)",
+			parallel_workers_launched,
+			parallel_workers_to_launch);
+}
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 38cb9e970d5..fe38758fd57 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -482,6 +482,7 @@ extern const struct config_enum_entry archive_mode_options[];
 extern const struct config_enum_entry recovery_target_action_options[];
 extern const struct config_enum_entry wal_sync_method_options[];
 extern const struct config_enum_entry dynamic_shared_memory_options[];
+extern const struct config_enum_entry log_parallel_workers_options[];
 
 /*
  * GUC option variables that are exported from this module
@@ -526,6 +527,7 @@ 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;
@@ -5236,6 +5238,16 @@ struct config_enum ConfigureNamesEnum[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"log_parallel_workers", PGC_SUSET, LOGGING_WHAT,
+			gettext_noop("Log information about parallel worker usage"),
+			NULL
+		},
+		&log_parallel_workers,
+		LOG_PARALLEL_WORKERS_NONE, log_parallel_workers_options,
+		NULL, NULL, NULL
+	},
+
 	/* End-of-list marker */
 	{
 		{NULL, 0, 0, NULL, NULL}, NULL, 0, NULL, NULL, NULL, NULL
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 079efa1baa7..94da28977cc 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -614,6 +614,7 @@
 #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 8811618acb7..a5bc98a3223 100644
--- a/src/include/access/parallel.h
+++ b/src/include/access/parallel.h
@@ -19,6 +19,20 @@
 #include "postmaster/bgworker.h"
 #include "storage/shm_mq.h"
 #include "storage/shm_toc.h"
+#include "utils/guc.h"
+
+typedef enum log_parallel_workers_option_list {
+	LOG_PARALLEL_WORKERS_NONE=0,
+	LOG_PARALLEL_WORKERS_ALL,
+	LOG_PARALLEL_WORKERS_SHORTAGE,
+} log_parallel_workers_option_list;
+
+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}
+};
 
 typedef void (*parallel_worker_main_type) (dsm_segment *seg, shm_toc *toc);
 
@@ -56,6 +70,7 @@ typedef struct ParallelWorkerContext
 extern PGDLLIMPORT volatile sig_atomic_t ParallelMessagePending;
 extern PGDLLIMPORT int ParallelWorkerNumber;
 extern PGDLLIMPORT bool InitializingParallelWorker;
+extern PGDLLEXPORT int log_parallel_workers;
 
 #define		IsParallelWorker()		(ParallelWorkerNumber >= 0)
 
@@ -78,4 +93,8 @@ 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 */
-- 
2.48.1