V4_0001-Add-a-guc-for-parallel-worker-logging.patch

From 907f83e81031c8faa839acdef5d07e57f046ade1 Mon Sep 17 00:00:00 2001
From: benoit <benoit.lobreau@dalibo.com>
Date: Tue, 8 Oct 2024 12:39:41 +0200
Subject: [PATCH 1/5] 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 `failures` 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         | 15 +++++++++++++++
 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, 65 insertions(+)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 934ef5e469..541b1a0f6e 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -7696,6 +7696,24 @@ 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 produced during the
+        execution of a parallel query or utility statement. The default value is
+        <literal>none</literal> which disables logging. <literal>all</literal> displays
+        information for all parallel queries, whereas <literal>failures</literal> displays
+        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 d4e84aabac..cfd73dc64e 100644
--- a/src/backend/access/transam/parallel.c
+++ b/src/backend/access/transam/parallel.c
@@ -1627,3 +1627,18 @@ LookupParallelWorkerFunction(const char *libraryname, const char *funcname)
 	return (parallel_worker_main_type)
 		load_external_function(libraryname, funcname, true, NULL);
 }
+
+/*
+ * The function determines if information about workers should
+ * be logged.
+*/
+bool
+LoggingParallelWorkers(int log_parallel_workers,
+					   int parallel_workers_to_launch,
+					   int parallel_workers_launched)
+{
+	return ((log_parallel_workers == LOG_PARALLEL_WORKERS_ALL &&
+			parallel_workers_to_launch > 0) ||
+			(log_parallel_workers == LOG_PARALLEL_WORKERS_FAILURE &&
+			parallel_workers_to_launch != parallel_workers_launched));
+}
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 2c4cc8cd41..94b6a237b1 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;
@@ -5196,6 +5198,16 @@ 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 667e0dc40a..7cd9c0f3f8 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -619,6 +619,7 @@
 #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, failure
 #log_timezone = 'GMT'
 
 # - Process Title -
diff --git a/src/include/access/parallel.h b/src/include/access/parallel.h
index 69ffe5498f..00aad1e742 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_FAILURE,
+} 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},
+	{"failure", LOG_PARALLEL_WORKERS_FAILURE, 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 bool LoggingParallelWorkers(int log_parallel_workers,
+								   int parallel_workers_to_launch,
+								   int parallel_workers_launched);
+
 #endif							/* PARALLEL_H */
-- 
2.46.2