GUC values - recommended way to declare the C variables?

From 8deac37278ba4388de7259d921e6e4e6385072a1 Mon Sep 17 00:00:00 2001
From: Peter Smith <peter.b.smith@fujitsu.com>
Date: Wed, 28 Sep 2022 09:48:33 +1000
Subject: [PATCH v1] Tidied some GUC C variable declarations.

Added comments to indicate the GUC variables.

Removed some unnecessary C variable assignments since the default values
will be assigned/overwritten by the GUC mechanism.
---
 src/backend/replication/logical/launcher.c |  5 +++--
 src/backend/replication/slot.c             |  6 +++---
 src/backend/replication/walsender.c        | 10 +++++-----
 3 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 3bbd522..66007ca 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -52,8 +52,9 @@
 /* max sleep time between cycles (3min) */
 #define DEFAULT_NAPTIME_PER_CYCLE 180000L
 
-int			max_logical_replication_workers = 4;
-int			max_sync_workers_per_subscription = 2;
+/* GUC variables. */
+int			max_logical_replication_workers;
+int			max_sync_workers_per_subscription;
 
 LogicalRepWorker *MyLogicalRepWorker = NULL;
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 0bd0031..b265fa8 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -97,9 +97,9 @@ ReplicationSlotCtlData *ReplicationSlotCtl = NULL;
 /* My backend's replication slot in the shared memory array */
 ReplicationSlot *MyReplicationSlot = NULL;
 
-/* GUCs */
-int			max_replication_slots = 0;	/* the maximum number of replication
-										 * slots */
+/* GUC variable. */
+int			max_replication_slots;	/* the maximum number of replication
+									 * slots */
 
 static void ReplicationSlotShmemExit(int code, Datum arg);
 static void ReplicationSlotDropAcquired(void);
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index e9ba500..e9c1429 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -118,12 +118,12 @@ bool		am_cascading_walsender = false; /* Am I cascading WAL to another
 											 * standby? */
 bool		am_db_walsender = false;	/* Connected to a database? */
 
-/* User-settable parameters for walsender */
-int			max_wal_senders = 0;	/* the maximum number of concurrent
+/* GUC variables. */
+int			max_wal_senders;		/* the maximum number of concurrent
 									 * walsenders */
-int			wal_sender_timeout = 60 * 1000; /* maximum time to send one WAL
-											 * data message */
-bool		log_replication_commands = false;
+int			wal_sender_timeout; 	/* maximum time to send one WAL
+									 * data message */
+bool		log_replication_commands;
 
 /*
  * State for WalSndWakeupRequest
-- 
1.8.3.1

From 3d58d6940ed6341e66d711c8d4e0aba2608e3cee Mon Sep 17 00:00:00 2001
From: Peter Smith <peter.b.smith@fujitsu.com>
Date: Thu, 20 Oct 2022 10:25:30 +1100
Subject: [PATCH v2] Tidied some GUC C variable declarations.

---
 src/backend/replication/logical/launcher.c | 1 +
 src/backend/replication/slot.c             | 6 +++---
 src/backend/replication/walsender.c        | 8 ++++----
 3 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index ff57421..6833eb9 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -52,6 +52,7 @@
 /* max sleep time between cycles (3min) */
 #define DEFAULT_NAPTIME_PER_CYCLE 180000L
 
+/* GUC variables. */
 int			max_logical_replication_workers = 4;
 int			max_sync_workers_per_subscription = 2;
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index d58d16e..5b73aa1 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -97,9 +97,9 @@ ReplicationSlotCtlData *ReplicationSlotCtl = NULL;
 /* My backend's replication slot in the shared memory array */
 ReplicationSlot *MyReplicationSlot = NULL;
 
-/* GUCs */
-int			max_replication_slots = 0;	/* the maximum number of replication
-										 * slots */
+/* GUC variable. */
+int			max_replication_slots = 10;	/* the maximum number of replication
+									 * slots */
 
 static void ReplicationSlotShmemExit(int code, Datum arg);
 static void ReplicationSlotDropAcquired(void);
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2193dca..142028a 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -118,11 +118,11 @@ bool		am_cascading_walsender = false; /* Am I cascading WAL to another
 											 * standby? */
 bool		am_db_walsender = false;	/* Connected to a database? */
 
-/* User-settable parameters for walsender */
-int			max_wal_senders = 0;	/* the maximum number of concurrent
+/* GUC variables. */
+int			max_wal_senders = 10;	/* the maximum number of concurrent
 									 * walsenders */
-int			wal_sender_timeout = 60 * 1000; /* maximum time to send one WAL
-											 * data message */
+int			wal_sender_timeout = 60 * 1000;	/* maximum time to send one WAL
+									 * data message */
 bool		log_replication_commands = false;
 
 /*
-- 
1.8.3.1

From 95c4e62158d6573c3a1413c53b2ecff7eb5e20ec Mon Sep 17 00:00:00 2001
From: Peter Smith <peter.b.smith@fujitsu.com>
Date: Thu, 20 Oct 2022 11:07:26 +1100
Subject: [PATCH v2] GUC C variable sanity check

Added a function to perform a sanity-check comparison of the C variable initial
value with the compiled-in default (boot_val). The purpose of this is to prevent
anybody reading those C declarations from being fooled by mismatched values.

Also fixed some existing mismatching values.
---
 src/backend/access/transam/xact.c   |  2 +-
 src/backend/access/transam/xlog.c   |  2 +-
 src/backend/libpq/be-secure.c       |  4 +-
 src/backend/storage/ipc/dsm_impl.c  |  2 +-
 src/backend/utils/adt/xml.c         |  4 +-
 src/backend/utils/cache/plancache.c |  2 +-
 src/backend/utils/error/elog.c      |  2 +-
 src/backend/utils/init/globals.c    |  4 +-
 src/backend/utils/misc/guc.c        | 74 +++++++++++++++++++++++++++++++++++++
 src/backend/utils/misc/guc_tables.c |  9 ++++-
 10 files changed, 92 insertions(+), 13 deletions(-)

diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index fd5103a..f45c95f 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -75,7 +75,7 @@
  *	User-tweakable parameters
  */
 int			DefaultXactIsoLevel = XACT_READ_COMMITTED;
-int			XactIsoLevel;
+int			XactIsoLevel = XACT_READ_COMMITTED;
 
 bool		DefaultXactReadOnly = false;
 bool		XactReadOnly;
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 27085b1..32e2b97 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -131,7 +131,7 @@ bool		wal_init_zero = true;
 bool		wal_recycle = true;
 bool		log_checkpoints = true;
 int			sync_method = DEFAULT_SYNC_METHOD;
-int			wal_level = WAL_LEVEL_MINIMAL;
+int			wal_level = WAL_LEVEL_REPLICA;
 int			CommitDelay = 0;	/* precommit delay in microseconds */
 int			CommitSiblings = 5; /* # concurrent xacts needed to sleep */
 int			wal_retrieve_retry_interval = 5000;
diff --git a/src/backend/libpq/be-secure.c b/src/backend/libpq/be-secure.c
index e3e5471..c896357 100644
--- a/src/backend/libpq/be-secure.c
+++ b/src/backend/libpq/be-secure.c
@@ -58,8 +58,8 @@ char	   *SSLECDHCurve;
 /* GUC variable: if false, prefer client ciphers */
 bool		SSLPreferServerCiphers;
 
-int			ssl_min_protocol_version;
-int			ssl_max_protocol_version;
+int			ssl_min_protocol_version = PG_TLS1_2_VERSION;
+int			ssl_max_protocol_version = PG_TLS_ANY;
 
 /* ------------------------------------------------------------ */
 /*			 Procedures common to all secure sessions			*/
diff --git a/src/backend/storage/ipc/dsm_impl.c b/src/backend/storage/ipc/dsm_impl.c
index e1b90c5..6ddd46a 100644
--- a/src/backend/storage/ipc/dsm_impl.c
+++ b/src/backend/storage/ipc/dsm_impl.c
@@ -109,7 +109,7 @@ const struct config_enum_entry dynamic_shared_memory_options[] = {
 };
 
 /* Implementation selector. */
-int			dynamic_shared_memory_type;
+int			dynamic_shared_memory_type = DEFAULT_DYNAMIC_SHARED_MEMORY_TYPE;
 
 /* Amount of space reserved for DSM segments in the main area. */
 int			min_dynamic_shared_memory;
diff --git a/src/backend/utils/adt/xml.c b/src/backend/utils/adt/xml.c
index d32cb11..8cd5262 100644
--- a/src/backend/utils/adt/xml.c
+++ b/src/backend/utils/adt/xml.c
@@ -94,8 +94,8 @@
 
 
 /* GUC variables */
-int			xmlbinary;
-int			xmloption;
+int			xmlbinary = XMLBINARY_BASE64;
+int			xmloption = XMLOPTION_CONTENT;
 
 #ifdef USE_LIBXML
 
diff --git a/src/backend/utils/cache/plancache.c b/src/backend/utils/cache/plancache.c
index 0d6a295..cc94320 100644
--- a/src/backend/utils/cache/plancache.c
+++ b/src/backend/utils/cache/plancache.c
@@ -116,7 +116,7 @@ static void PlanCacheObjectCallback(Datum arg, int cacheid, uint32 hashvalue);
 static void PlanCacheSysCallback(Datum arg, int cacheid, uint32 hashvalue);
 
 /* GUC parameter */
-int			plan_cache_mode;
+int			plan_cache_mode = PLAN_CACHE_MODE_AUTO;
 
 /*
  * InitPlanCache: initialize module during InitPostgres.
diff --git a/src/backend/utils/error/elog.c b/src/backend/utils/error/elog.c
index 6e0a66c..2585e24 100644
--- a/src/backend/utils/error/elog.c
+++ b/src/backend/utils/error/elog.c
@@ -107,7 +107,7 @@ extern bool redirection_done;
 emit_log_hook_type emit_log_hook = NULL;
 
 /* GUC parameters */
-int			Log_error_verbosity = PGERROR_VERBOSE;
+int			Log_error_verbosity = PGERROR_DEFAULT;
 char	   *Log_line_prefix = NULL; /* format for extra log line info */
 int			Log_destination = LOG_DESTINATION_STDERR;
 char	   *Log_destination_string = NULL;
diff --git a/src/backend/utils/init/globals.c b/src/backend/utils/init/globals.c
index 1a5d29a..00bceec 100644
--- a/src/backend/utils/init/globals.c
+++ b/src/backend/utils/init/globals.c
@@ -133,8 +133,8 @@ int			max_parallel_maintenance_workers = 2;
  * MaxBackends is computed by PostmasterMain after modules have had a chance to
  * register background workers.
  */
-int			NBuffers = 1000;
-int			MaxConnections = 90;
+int			NBuffers = 16384;
+int			MaxConnections = 100;
 int			max_worker_processes = 8;
 int			max_parallel_workers = 8;
 int			MaxBackends = 0;
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 6f21752..f138798 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -1382,6 +1382,76 @@ check_GUC_name_for_parameter_acl(const char *name)
 	return false;
 }
 
+#ifdef USE_ASSERT_CHECKING
+/*
+ * A GUC C variable can be declared with an initial value, but the GUC mechanism
+ * will overwrite that using the compiled-in default (boot_val) as per
+ * guc_tables.c.
+ *
+ * This function performs a sanity-check comparison of the C variable initial
+ * value with the boot_val, to prevent anybody reading those C declarations
+ * from being fooled by mismatched values.
+ *
+ * GUC C variable declared value:
+ * bool - can be false, otherwise must be same as the boot_val
+ * int  - can be 0, otherwise must be same as the boot_val
+ * real - can be 0.0, otherwise must be same as the boot_val
+ * string - can be NULL, otherwise must be strcmp equal to the boot_val
+ * enum - must be same as the boot_val
+ */
+static void
+sanity_check_GUC_C_var(struct config_generic *gconf)
+{
+	switch (gconf->vartype)
+	{
+		case PGC_BOOL:
+			{
+				struct config_bool *conf = (struct config_bool *) gconf;
+
+				if (*conf->variable && !conf->boot_val)
+					elog(FATAL, "GUC (PGC_BOOL) %s, boot_val=%d, C-var=%d",
+						 conf->gen.name, conf->boot_val, *conf->variable);
+				break;
+			}
+		case PGC_INT:
+			{
+				struct config_int *conf = (struct config_int *) gconf;
+
+				if (*conf->variable != 0 && *conf->variable != conf->boot_val)
+					elog(FATAL, "GUC (PGC_INT) %s, boot_val=%d, C-var=%d",
+						 conf->gen.name, conf->boot_val, *conf->variable);
+				break;
+			}
+		case PGC_REAL:
+			{
+				struct config_real *conf = (struct config_real *) gconf;
+
+				if (*conf->variable != 0.0 && *conf->variable != conf->boot_val)
+					elog(FATAL, "GUC (PGC_REAL) %s, boot_val=%g, C-var=%g",
+						 conf->gen.name, conf->boot_val, *conf->variable);
+				break;
+			}
+		case PGC_STRING:
+			{
+				struct config_string *conf = (struct config_string *) gconf;
+
+				if (*conf->variable != NULL && strcmp(*conf->variable, conf->boot_val) != 0)
+					elog(FATAL, "GUC (PGC_STRING) %s, boot_val=%s, C-var=%s",
+						 conf->gen.name, conf->boot_val ? conf->boot_val : "<null>", *conf->variable);
+				break;
+			}
+		case PGC_ENUM:
+			{
+				struct config_enum *conf = (struct config_enum *) gconf;
+
+				if (*conf->variable != conf->boot_val)
+					elog(FATAL, "GUC (PGC_ENUM) %s, boot_val=%d, C-var=%d",
+						 conf->gen.name, conf->boot_val, *conf->variable);
+				break;
+			}
+	}
+}
+#endif
 
 /*
  * Initialize GUC options during program startup.
@@ -1413,6 +1483,10 @@ InitializeGUCOptions(void)
 	hash_seq_init(&status, guc_hashtab);
 	while ((hentry = (GUCHashEntry *) hash_seq_search(&status)) != NULL)
 	{
+#ifdef USE_ASSERT_CHECKING
+		sanity_check_GUC_C_var(hentry->gucvar);
+#endif
+
 		InitializeOneGUCOption(hentry->gucvar);
 	}
 
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 05ab087..23a1b0d 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -526,7 +526,7 @@ int			ssl_renegotiation_limit;
  * This really belongs in pg_shmem.c, but is defined here so that it doesn't
  * need to be duplicated in all the different implementations of pg_shmem.c.
  */
-int			huge_pages;
+int			huge_pages = HUGE_PAGES_TRY;
 int			huge_page_size;
 
 /*
@@ -543,7 +543,12 @@ static char *locale_ctype;
 static char *server_encoding_string;
 static char *server_version_string;
 static int	server_version_num;
-static int	syslog_facility;
+static int	syslog_facility =
+#ifdef HAVE_SYSLOG
+		LOG_LOCAL0;
+#else
+		0;
+#endif
 static char *timezone_string;
 static char *log_timezone_string;
 static char *timezone_abbreviations_string;
-- 
1.8.3.1

From 5f8cb9daba5e7b50e4b8fae8de101077bd2eac17 Mon Sep 17 00:00:00 2001
From: Peter Smith <peter.b.smith@fujitsu.com>
Date: Tue, 25 Oct 2022 14:30:41 +1100
Subject: [PATCH v3] GUC C variable sanity check

Added a function to perform a sanity-check comparison of the C variable initial
value with the compiled-in default (boot_val). The purpose of this is to prevent
anybody reading those C declarations from being fooled by mismatched values.

Also fixed some existing mismatching values.

Checking is skipped for GUCs flagged as compiler-dependent (GUC_DEFAULT_COMPILE).
---
 src/backend/access/transam/xact.c   |  2 +-
 src/backend/access/transam/xlog.c   |  2 +-
 src/backend/libpq/be-secure.c       |  4 +-
 src/backend/utils/adt/xml.c         |  4 +-
 src/backend/utils/cache/plancache.c |  2 +-
 src/backend/utils/error/elog.c      |  2 +-
 src/backend/utils/init/globals.c    |  4 +-
 src/backend/utils/misc/guc.c        | 78 +++++++++++++++++++++++++++++++++++++
 src/backend/utils/misc/guc_tables.c |  2 +-
 9 files changed, 89 insertions(+), 11 deletions(-)

diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index fd5103a..f45c95f 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -75,7 +75,7 @@
  *	User-tweakable parameters
  */
 int			DefaultXactIsoLevel = XACT_READ_COMMITTED;
-int			XactIsoLevel;
+int			XactIsoLevel = XACT_READ_COMMITTED;
 
 bool		DefaultXactReadOnly = false;
 bool		XactReadOnly;
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 8f10eff..be54c23 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -131,7 +131,7 @@ bool		wal_init_zero = true;
 bool		wal_recycle = true;
 bool		log_checkpoints = true;
 int			sync_method = DEFAULT_SYNC_METHOD;
-int			wal_level = WAL_LEVEL_MINIMAL;
+int			wal_level = WAL_LEVEL_REPLICA;
 int			CommitDelay = 0;	/* precommit delay in microseconds */
 int			CommitSiblings = 5; /* # concurrent xacts needed to sleep */
 int			wal_retrieve_retry_interval = 5000;
diff --git a/src/backend/libpq/be-secure.c b/src/backend/libpq/be-secure.c
index e3e5471..c896357 100644
--- a/src/backend/libpq/be-secure.c
+++ b/src/backend/libpq/be-secure.c
@@ -58,8 +58,8 @@ char	   *SSLECDHCurve;
 /* GUC variable: if false, prefer client ciphers */
 bool		SSLPreferServerCiphers;
 
-int			ssl_min_protocol_version;
-int			ssl_max_protocol_version;
+int			ssl_min_protocol_version = PG_TLS1_2_VERSION;
+int			ssl_max_protocol_version = PG_TLS_ANY;
 
 /* ------------------------------------------------------------ */
 /*			 Procedures common to all secure sessions			*/
diff --git a/src/backend/utils/adt/xml.c b/src/backend/utils/adt/xml.c
index d32cb11..8cd5262 100644
--- a/src/backend/utils/adt/xml.c
+++ b/src/backend/utils/adt/xml.c
@@ -94,8 +94,8 @@
 
 
 /* GUC variables */
-int			xmlbinary;
-int			xmloption;
+int			xmlbinary = XMLBINARY_BASE64;
+int			xmloption = XMLOPTION_CONTENT;
 
 #ifdef USE_LIBXML
 
diff --git a/src/backend/utils/cache/plancache.c b/src/backend/utils/cache/plancache.c
index 0d6a295..cc94320 100644
--- a/src/backend/utils/cache/plancache.c
+++ b/src/backend/utils/cache/plancache.c
@@ -116,7 +116,7 @@ static void PlanCacheObjectCallback(Datum arg, int cacheid, uint32 hashvalue);
 static void PlanCacheSysCallback(Datum arg, int cacheid, uint32 hashvalue);
 
 /* GUC parameter */
-int			plan_cache_mode;
+int			plan_cache_mode = PLAN_CACHE_MODE_AUTO;
 
 /*
  * InitPlanCache: initialize module during InitPostgres.
diff --git a/src/backend/utils/error/elog.c b/src/backend/utils/error/elog.c
index 6e0a66c..2585e24 100644
--- a/src/backend/utils/error/elog.c
+++ b/src/backend/utils/error/elog.c
@@ -107,7 +107,7 @@ extern bool redirection_done;
 emit_log_hook_type emit_log_hook = NULL;
 
 /* GUC parameters */
-int			Log_error_verbosity = PGERROR_VERBOSE;
+int			Log_error_verbosity = PGERROR_DEFAULT;
 char	   *Log_line_prefix = NULL; /* format for extra log line info */
 int			Log_destination = LOG_DESTINATION_STDERR;
 char	   *Log_destination_string = NULL;
diff --git a/src/backend/utils/init/globals.c b/src/backend/utils/init/globals.c
index 1a5d29a..00bceec 100644
--- a/src/backend/utils/init/globals.c
+++ b/src/backend/utils/init/globals.c
@@ -133,8 +133,8 @@ int			max_parallel_maintenance_workers = 2;
  * MaxBackends is computed by PostmasterMain after modules have had a chance to
  * register background workers.
  */
-int			NBuffers = 1000;
-int			MaxConnections = 90;
+int			NBuffers = 16384;
+int			MaxConnections = 100;
 int			max_worker_processes = 8;
 int			max_parallel_workers = 8;
 int			MaxBackends = 0;
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 6f21752..9e19a3e 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -1382,6 +1382,80 @@ check_GUC_name_for_parameter_acl(const char *name)
 	return false;
 }
 
+#ifdef USE_ASSERT_CHECKING
+/*
+ * A GUC C variable can be declared with an initial value, but the GUC mechanism
+ * will overwrite that using the compiled-in default (boot_val) as per
+ * guc_tables.c.
+ *
+ * This function performs a sanity-check comparison of the C variable initial
+ * value with the boot_val, to prevent anybody reading those C declarations
+ * from being fooled by mismatched values.
+ *
+ * GUC C variable validation rules:
+ * bool - can be false, otherwise must be same as the boot_val
+ * int  - can be 0, otherwise must be same as the boot_val
+ * real - can be 0.0, otherwise must be same as the boot_val
+ * string - can be NULL, otherwise must be strcmp equal to the boot_val
+ * enum - must be same as the boot_val
+ */
+static void
+sanity_check_GUC_C_var(struct config_generic *gconf)
+{
+	/* Skip checking for dynamic (compiler-dependent) GUCs. */
+	if (gconf->flags & GUC_DEFAULT_COMPILE)
+		return;
+
+	switch (gconf->vartype)
+	{
+		case PGC_BOOL:
+			{
+				struct config_bool *conf = (struct config_bool *) gconf;
+
+				if (*conf->variable && !conf->boot_val)
+					elog(FATAL, "GUC (PGC_BOOL) %s, boot_val=%d, C-var=%d",
+						 conf->gen.name, conf->boot_val, *conf->variable);
+				break;
+			}
+		case PGC_INT:
+			{
+				struct config_int *conf = (struct config_int *) gconf;
+
+				if (*conf->variable != 0 && *conf->variable != conf->boot_val)
+					elog(FATAL, "GUC (PGC_INT) %s, boot_val=%d, C-var=%d",
+						 conf->gen.name, conf->boot_val, *conf->variable);
+				break;
+			}
+		case PGC_REAL:
+			{
+				struct config_real *conf = (struct config_real *) gconf;
+
+				if (*conf->variable != 0.0 && *conf->variable != conf->boot_val)
+					elog(FATAL, "GUC (PGC_REAL) %s, boot_val=%g, C-var=%g",
+						 conf->gen.name, conf->boot_val, *conf->variable);
+				break;
+			}
+		case PGC_STRING:
+			{
+				struct config_string *conf = (struct config_string *) gconf;
+
+				if (*conf->variable != NULL && strcmp(*conf->variable, conf->boot_val) != 0)
+					elog(FATAL, "GUC (PGC_STRING) %s, boot_val=%s, C-var=%s",
+						 conf->gen.name, conf->boot_val ? conf->boot_val : "<null>", *conf->variable);
+				break;
+			}
+		case PGC_ENUM:
+			{
+				struct config_enum *conf = (struct config_enum *) gconf;
+
+				if (*conf->variable != conf->boot_val)
+					elog(FATAL, "GUC (PGC_ENUM) %s, boot_val=%d, C-var=%d",
+						 conf->gen.name, conf->boot_val, *conf->variable);
+				break;
+			}
+	}
+}
+#endif
 
 /*
  * Initialize GUC options during program startup.
@@ -1413,6 +1487,10 @@ InitializeGUCOptions(void)
 	hash_seq_init(&status, guc_hashtab);
 	while ((hentry = (GUCHashEntry *) hash_seq_search(&status)) != NULL)
 	{
+#ifdef USE_ASSERT_CHECKING
+		sanity_check_GUC_C_var(hentry->gucvar);
+#endif
+
 		InitializeOneGUCOption(hentry->gucvar);
 	}
 
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 871be3e..0ff2b67 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -526,7 +526,7 @@ int			ssl_renegotiation_limit;
  * This really belongs in pg_shmem.c, but is defined here so that it doesn't
  * need to be duplicated in all the different implementations of pg_shmem.c.
  */
-int			huge_pages;
+int			huge_pages = HUGE_PAGES_TRY;
 int			huge_page_size;
 
 /*
-- 
1.8.3.1

From 841cd2e64b8a8033e2e2953a9b14da9401dd497c Mon Sep 17 00:00:00 2001
From: Peter Smith <peter.b.smith@fujitsu.com>
Date: Tue, 25 Oct 2022 10:10:58 +1100
Subject: [PATCH v3] GUC - tidy some C variable declarations.

---
 src/backend/replication/logical/launcher.c | 1 +
 src/backend/replication/slot.c             | 6 +++---
 src/backend/replication/walsender.c        | 4 ++--
 3 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index f2c55f3..c6d8376 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -52,6 +52,7 @@
 /* max sleep time between cycles (3min) */
 #define DEFAULT_NAPTIME_PER_CYCLE 180000L
 
+/* GUC variables. */
 int			max_logical_replication_workers = 4;
 int			max_sync_workers_per_subscription = 2;
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index d58d16e..5b73aa1 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -97,9 +97,9 @@ ReplicationSlotCtlData *ReplicationSlotCtl = NULL;
 /* My backend's replication slot in the shared memory array */
 ReplicationSlot *MyReplicationSlot = NULL;
 
-/* GUCs */
-int			max_replication_slots = 0;	/* the maximum number of replication
-										 * slots */
+/* GUC variable. */
+int			max_replication_slots = 10;	/* the maximum number of replication
+									 * slots */
 
 static void ReplicationSlotShmemExit(int code, Datum arg);
 static void ReplicationSlotDropAcquired(void);
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2193dca..3faae4a 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -118,8 +118,8 @@ bool		am_cascading_walsender = false; /* Am I cascading WAL to another
 											 * standby? */
 bool		am_db_walsender = false;	/* Connected to a database? */
 
-/* User-settable parameters for walsender */
-int			max_wal_senders = 0;	/* the maximum number of concurrent
+/* GUC variables. */
+int			max_wal_senders = 10;	/* the maximum number of concurrent
 									 * walsenders */
 int			wal_sender_timeout = 60 * 1000; /* maximum time to send one WAL
 											 * data message */
-- 
1.8.3.1

From 02abb26f30a262137b48d87945932d42342ff535 Mon Sep 17 00:00:00 2001
From: Peter Smith <peter.b.smith@fujitsu.com>
Date: Tue, 25 Oct 2022 11:07:56 +1100
Subject: [PATCH v3] TMP - Justins DYNAMIC_DEFAULT patch.

From 24/10 attachment: https://www.postgresql.org/message-id/20221024220544.GJ16921%40telsasoft.com
---
 doc/src/sgml/func.sgml              | 15 +++++++
 src/backend/utils/misc/guc_funcs.c  |  6 ++-
 src/backend/utils/misc/guc_tables.c | 78 +++++++++++++++++++++++--------------
 src/include/utils/guc.h             |  2 +
 4 files changed, 70 insertions(+), 31 deletions(-)

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 6e0425c..b8e0507 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -24374,6 +24374,21 @@ SELECT collation for ('foo' COLLATE "de_DE");
      <row><entry>Flag</entry><entry>Description</entry></row>
     </thead>
     <tbody>
+
+     <row>
+      <entry><literal>DEFAULT_COMPILE</literal></entry>
+      <entry>Parameters with this flag have default values which vary by
+      platform, or compile-time options.
+      </entry>
+     </row>
+
+     <row>
+      <entry><literal>DEFAULT_INITDB</literal></entry>
+      <entry>Parameters with this flag have default values which are
+      determined dynamically during initdb.
+      </entry>
+     </row>
+
      <row>
       <entry><literal>EXPLAIN</literal></entry>
       <entry>Parameters with this flag are included in
diff --git a/src/backend/utils/misc/guc_funcs.c b/src/backend/utils/misc/guc_funcs.c
index 108b3bd..2b666e8 100644
--- a/src/backend/utils/misc/guc_funcs.c
+++ b/src/backend/utils/misc/guc_funcs.c
@@ -538,7 +538,7 @@ ShowAllGUCConfig(DestReceiver *dest)
 Datum
 pg_settings_get_flags(PG_FUNCTION_ARGS)
 {
-#define MAX_GUC_FLAGS	6
+#define MAX_GUC_FLAGS	8
 	char	   *varname = TextDatumGetCString(PG_GETARG_DATUM(0));
 	struct config_generic *record;
 	int			cnt = 0;
@@ -551,6 +551,10 @@ pg_settings_get_flags(PG_FUNCTION_ARGS)
 	if (record == NULL)
 		PG_RETURN_NULL();
 
+	if (record->flags & GUC_DEFAULT_COMPILE)
+		flags[cnt++] = CStringGetTextDatum("DEFAULT_COMPILE");
+	if (record->flags & GUC_DEFAULT_INITDB)
+		flags[cnt++] = CStringGetTextDatum("DEFAULT_INITDB");
 	if (record->flags & GUC_EXPLAIN)
 		flags[cnt++] = CStringGetTextDatum("EXPLAIN");
 	if (record->flags & GUC_NO_RESET)
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 05ab087..871be3e 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -600,7 +600,7 @@ StaticAssertDecl(lengthof(GucContext_Names) == (PGC_USERSET + 1),
 const char *const GucSource_Names[] =
 {
 	 /* PGC_S_DEFAULT */ "default",
-	 /* PGC_S_DYNAMIC_DEFAULT */ "default",
+	 /* PGC_S_DYNAMIC_DEFAULT */ "default", //
 	 /* PGC_S_ENV_VAR */ "environment variable",
 	 /* PGC_S_FILE */ "configuration file",
 	 /* PGC_S_ARGV */ "command line",
@@ -1178,7 +1178,7 @@ struct config_bool ConfigureNamesBool[] =
 		{"debug_assertions", PGC_INTERNAL, PRESET_OPTIONS,
 			gettext_noop("Shows whether the running server has assertion checks enabled."),
 			NULL,
-			GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+			GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE | GUC_DEFAULT_COMPILE
 		},
 		&assert_enabled,
 #ifdef USE_ASSERT_CHECKING
@@ -1354,7 +1354,8 @@ struct config_bool ConfigureNamesBool[] =
 	{
 		{"update_process_title", PGC_SUSET, PROCESS_TITLE,
 			gettext_noop("Updates the process title to show the active SQL command."),
-			gettext_noop("Enables updating of the process title every time a new SQL command is received by the server.")
+			gettext_noop("Enables updating of the process title every time a new SQL command is received by the server."),
+			GUC_DEFAULT_COMPILE
 		},
 		&update_process_title,
 #ifdef WIN32
@@ -2103,7 +2104,8 @@ struct config_int ConfigureNamesInt[] =
 	{
 		{"max_connections", PGC_POSTMASTER, CONN_AUTH_SETTINGS,
 			gettext_noop("Sets the maximum number of concurrent connections."),
-			NULL
+			NULL,
+			GUC_DEFAULT_INITDB
 		},
 		&MaxConnections,
 		100, 1, MAX_BACKENDS,
@@ -2140,7 +2142,7 @@ struct config_int ConfigureNamesInt[] =
 		{"shared_buffers", PGC_POSTMASTER, RESOURCES_MEM,
 			gettext_noop("Sets the number of shared memory buffers used by the server."),
 			NULL,
-			GUC_UNIT_BLOCKS
+			GUC_UNIT_BLOCKS | GUC_DEFAULT_INITDB
 		},
 		&NBuffers,
 		16384, 16, INT_MAX / 2,
@@ -2183,7 +2185,8 @@ struct config_int ConfigureNamesInt[] =
 	{
 		{"port", PGC_POSTMASTER, CONN_AUTH_SETTINGS,
 			gettext_noop("Sets the TCP port the server listens on."),
-			NULL
+			NULL,
+			GUC_DEFAULT_COMPILE
 		},
 		&PostPortNumber,
 		DEF_PGPORT, 1, 65535,
@@ -2212,7 +2215,8 @@ struct config_int ConfigureNamesInt[] =
 						 "to be a numeric mode specification in the form "
 						 "accepted by the chmod and umask system calls. "
 						 "(To use the customary octal format the number must "
-						 "start with a 0 (zero).)")
+						 "start with a 0 (zero).)"),
+			GUC_DEFAULT_INITDB
 		},
 		&Log_file_mode,
 		0600, 0000, 0777,
@@ -2654,7 +2658,7 @@ struct config_int ConfigureNamesInt[] =
 		{"checkpoint_flush_after", PGC_SIGHUP, WAL_CHECKPOINTS,
 			gettext_noop("Number of pages after which previously performed writes are flushed to disk."),
 			NULL,
-			GUC_UNIT_BLOCKS
+			GUC_UNIT_BLOCKS | GUC_DEFAULT_COMPILE
 		},
 		&checkpoint_flush_after,
 		DEFAULT_CHECKPOINT_FLUSH_AFTER, 0, WRITEBACK_MAX_PENDING_FLUSHES,
@@ -2872,7 +2876,7 @@ struct config_int ConfigureNamesInt[] =
 		{"bgwriter_flush_after", PGC_SIGHUP, RESOURCES_BGWRITER,
 			gettext_noop("Number of pages after which previously performed writes are flushed to disk."),
 			NULL,
-			GUC_UNIT_BLOCKS
+			GUC_UNIT_BLOCKS | GUC_DEFAULT_COMPILE
 		},
 		&bgwriter_flush_after,
 		DEFAULT_BGWRITER_FLUSH_AFTER, 0, WRITEBACK_MAX_PENDING_FLUSHES,
@@ -2885,7 +2889,7 @@ struct config_int ConfigureNamesInt[] =
 			RESOURCES_ASYNCHRONOUS,
 			gettext_noop("Number of simultaneous requests that can be handled efficiently by the disk subsystem."),
 			NULL,
-			GUC_EXPLAIN
+			GUC_EXPLAIN | GUC_DEFAULT_COMPILE
 		},
 		&effective_io_concurrency,
 #ifdef USE_PREFETCH
@@ -2903,7 +2907,7 @@ struct config_int ConfigureNamesInt[] =
 			RESOURCES_ASYNCHRONOUS,
 			gettext_noop("A variant of effective_io_concurrency that is used for maintenance work."),
 			NULL,
-			GUC_EXPLAIN
+			GUC_EXPLAIN | GUC_DEFAULT_COMPILE
 		},
 		&maintenance_io_concurrency,
 #ifdef USE_PREFETCH
@@ -2920,7 +2924,7 @@ struct config_int ConfigureNamesInt[] =
 		{"backend_flush_after", PGC_USERSET, RESOURCES_ASYNCHRONOUS,
 			gettext_noop("Number of pages after which previously performed writes are flushed to disk."),
 			NULL,
-			GUC_UNIT_BLOCKS
+			GUC_UNIT_BLOCKS | GUC_DEFAULT_COMPILE
 		},
 		&backend_flush_after,
 		DEFAULT_BACKEND_FLUSH_AFTER, 0, WRITEBACK_MAX_PENDING_FLUSHES,
@@ -3363,7 +3367,7 @@ struct config_int ConfigureNamesInt[] =
 		{"debug_discard_caches", PGC_SUSET, DEVELOPER_OPTIONS,
 			gettext_noop("Aggressively flush system caches for debugging purposes."),
 			NULL,
-			GUC_NOT_IN_SAMPLE
+			GUC_NOT_IN_SAMPLE | GUC_DEFAULT_COMPILE
 		},
 		&debug_discard_caches,
 #ifdef DISCARD_CACHES_ENABLED
@@ -3856,7 +3860,8 @@ struct config_string ConfigureNamesString[] =
 	{
 		{"log_timezone", PGC_SIGHUP, LOGGING_WHAT,
 			gettext_noop("Sets the time zone to use in log messages."),
-			NULL
+			NULL,
+			GUC_DEFAULT_INITDB
 		},
 		&log_timezone_string,
 		"GMT",
@@ -3868,7 +3873,7 @@ struct config_string ConfigureNamesString[] =
 			gettext_noop("Sets the display format for date and time values."),
 			gettext_noop("Also controls interpretation of ambiguous "
 						 "date inputs."),
-			GUC_LIST_INPUT | GUC_REPORT
+			GUC_LIST_INPUT | GUC_REPORT | GUC_DEFAULT_INITDB
 		},
 		&datestyle_string,
 		"ISO, MDY",
@@ -3970,7 +3975,8 @@ struct config_string ConfigureNamesString[] =
 	{
 		{"lc_messages", PGC_SUSET, CLIENT_CONN_LOCALE,
 			gettext_noop("Sets the language in which messages are displayed."),
-			NULL
+			NULL,
+			GUC_DEFAULT_INITDB
 		},
 		&locale_messages,
 		"",
@@ -3980,7 +3986,8 @@ struct config_string ConfigureNamesString[] =
 	{
 		{"lc_monetary", PGC_USERSET, CLIENT_CONN_LOCALE,
 			gettext_noop("Sets the locale for formatting monetary amounts."),
-			NULL
+			NULL,
+			GUC_DEFAULT_INITDB
 		},
 		&locale_monetary,
 		"C",
@@ -3990,7 +3997,8 @@ struct config_string ConfigureNamesString[] =
 	{
 		{"lc_numeric", PGC_USERSET, CLIENT_CONN_LOCALE,
 			gettext_noop("Sets the locale for formatting numbers."),
-			NULL
+			NULL,
+			GUC_DEFAULT_INITDB
 		},
 		&locale_numeric,
 		"C",
@@ -4000,7 +4008,8 @@ struct config_string ConfigureNamesString[] =
 	{
 		{"lc_time", PGC_USERSET, CLIENT_CONN_LOCALE,
 			gettext_noop("Sets the locale for formatting date and time values."),
-			NULL
+			NULL,
+			GUC_DEFAULT_INITDB
 		},
 		&locale_time,
 		"C",
@@ -4159,7 +4168,8 @@ struct config_string ConfigureNamesString[] =
 		{"TimeZone", PGC_USERSET, CLIENT_CONN_LOCALE,
 			gettext_noop("Sets the time zone for displaying and interpreting time stamps."),
 			NULL,
-			GUC_REPORT
+			GUC_REPORT | GUC_DEFAULT_INITDB
+
 		},
 		&timezone_string,
 		"GMT",
@@ -4190,7 +4200,7 @@ struct config_string ConfigureNamesString[] =
 		{"unix_socket_directories", PGC_POSTMASTER, CONN_AUTH_SETTINGS,
 			gettext_noop("Sets the directories where Unix-domain sockets will be created."),
 			NULL,
-			GUC_LIST_INPUT | GUC_LIST_QUOTE | GUC_SUPERUSER_ONLY
+			GUC_LIST_INPUT | GUC_LIST_QUOTE | GUC_SUPERUSER_ONLY | GUC_DEFAULT_COMPILE
 		},
 		&Unix_socket_directories,
 		DEFAULT_PGSOCKET_DIR,
@@ -4271,7 +4281,7 @@ struct config_string ConfigureNamesString[] =
 		{"ssl_library", PGC_INTERNAL, PRESET_OPTIONS,
 			gettext_noop("Shows the name of the SSL library."),
 			NULL,
-			GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+			GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE | GUC_DEFAULT_COMPILE
 		},
 		&ssl_library,
 #ifdef USE_SSL
@@ -4346,7 +4356,9 @@ struct config_string ConfigureNamesString[] =
 	{
 		{"default_text_search_config", PGC_USERSET, CLIENT_CONN_LOCALE,
 			gettext_noop("Sets default text search configuration."),
-			NULL
+			NULL,
+			GUC_DEFAULT_INITDB
+
 		},
 		&TSCurrentConfig,
 		"pg_catalog.simple",
@@ -4357,7 +4369,7 @@ struct config_string ConfigureNamesString[] =
 		{"ssl_ciphers", PGC_SIGHUP, CONN_AUTH_SSL,
 			gettext_noop("Sets the list of allowed SSL ciphers."),
 			NULL,
-			GUC_SUPERUSER_ONLY
+			GUC_SUPERUSER_ONLY | GUC_DEFAULT_COMPILE
 		},
 		&SSLCipherSuites,
 #ifdef USE_OPENSSL
@@ -4372,7 +4384,7 @@ struct config_string ConfigureNamesString[] =
 		{"ssl_ecdh_curve", PGC_SIGHUP, CONN_AUTH_SSL,
 			gettext_noop("Sets the curve to use for ECDH."),
 			NULL,
-			GUC_SUPERUSER_ONLY
+			GUC_SUPERUSER_ONLY | GUC_DEFAULT_COMPILE
 		},
 		&SSLECDHCurve,
 #ifdef USE_SSL
@@ -4610,7 +4622,8 @@ struct config_enum ConfigureNamesEnum[] =
 	{
 		{"syslog_facility", PGC_SIGHUP, LOGGING_WHERE,
 			gettext_noop("Sets the syslog \"facility\" to be used when syslog enabled."),
-			NULL
+			NULL,
+			GUC_DEFAULT_COMPILE
 		},
 		&syslog_facility,
 #ifdef HAVE_SYSLOG
@@ -4723,7 +4736,9 @@ struct config_enum ConfigureNamesEnum[] =
 	{
 		{"dynamic_shared_memory_type", PGC_POSTMASTER, RESOURCES_MEM,
 			gettext_noop("Selects the dynamic shared memory implementation used."),
-			NULL
+			NULL,
+			/* platform-specific default, which is also overriden during initdb */
+			GUC_DEFAULT_COMPILE | GUC_DEFAULT_INITDB
 		},
 		&dynamic_shared_memory_type,
 		DEFAULT_DYNAMIC_SHARED_MEMORY_TYPE, dynamic_shared_memory_options,
@@ -4733,7 +4748,8 @@ struct config_enum ConfigureNamesEnum[] =
 	{
 		{"shared_memory_type", PGC_POSTMASTER, RESOURCES_MEM,
 			gettext_noop("Selects the shared memory implementation used for the main shared memory region."),
-			NULL
+			NULL,
+			GUC_DEFAULT_COMPILE
 		},
 		&shared_memory_type,
 		DEFAULT_SHARED_MEMORY_TYPE, shared_memory_options,
@@ -4743,7 +4759,8 @@ struct config_enum ConfigureNamesEnum[] =
 	{
 		{"wal_sync_method", PGC_SIGHUP, WAL_SETTINGS,
 			gettext_noop("Selects the method used for forcing WAL updates to disk."),
-			NULL
+			NULL,
+			GUC_DEFAULT_COMPILE
 		},
 		&sync_method,
 		DEFAULT_SYNC_METHOD, sync_method_options,
@@ -4805,7 +4822,8 @@ struct config_enum ConfigureNamesEnum[] =
 	{
 		{"password_encryption", PGC_USERSET, CONN_AUTH_AUTH,
 			gettext_noop("Chooses the algorithm for encrypting passwords."),
-			NULL
+			NULL,
+			GUC_DEFAULT_INITDB
 		},
 		&Password_encryption,
 		PASSWORD_TYPE_SCRAM_SHA_256, password_encryption_options,
diff --git a/src/include/utils/guc.h b/src/include/utils/guc.h
index b3aaff9..7905358 100644
--- a/src/include/utils/guc.h
+++ b/src/include/utils/guc.h
@@ -221,6 +221,8 @@ typedef enum
 #define GUC_DISALLOW_IN_AUTO_FILE \
 							   0x002000 /* can't set in PG_AUTOCONF_FILENAME */
 #define GUC_RUNTIME_COMPUTED   0x004000 /* delay processing in 'postgres -C' */
+#define GUC_DEFAULT_COMPILE	   0x008000	/* default is determined at compile time */
+#define GUC_DEFAULT_INITDB	   0x010000	/* default is determined at during initdb */
 
 #define GUC_UNIT_KB			 0x01000000 /* value is in kilobytes */
 #define GUC_UNIT_BLOCKS		 0x02000000 /* value is in blocks */
-- 
1.8.3.1

From 896d322a671d395dd5b51572d6c91ce4759f0f99 Mon Sep 17 00:00:00 2001
From: Peter Smith <peter.b.smith@fujitsu.com>
Date: Tue, 25 Oct 2022 16:56:47 +1100
Subject: [PATCH v4] TMP - Justins DYNAMIC_DEFAULT patch.

From 24/10 attachment: https://www.postgresql.org/message-id/20221024220544.GJ16921%40telsasoft.com
---
 doc/src/sgml/func.sgml              | 15 +++++++
 src/backend/utils/misc/guc_funcs.c  |  6 ++-
 src/backend/utils/misc/guc_tables.c | 78 +++++++++++++++++++++++--------------
 src/include/utils/guc.h             |  2 +
 4 files changed, 70 insertions(+), 31 deletions(-)

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 6e0425c..b8e0507 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -24374,6 +24374,21 @@ SELECT collation for ('foo' COLLATE "de_DE");
      <row><entry>Flag</entry><entry>Description</entry></row>
     </thead>
     <tbody>
+
+     <row>
+      <entry><literal>DEFAULT_COMPILE</literal></entry>
+      <entry>Parameters with this flag have default values which vary by
+      platform, or compile-time options.
+      </entry>
+     </row>
+
+     <row>
+      <entry><literal>DEFAULT_INITDB</literal></entry>
+      <entry>Parameters with this flag have default values which are
+      determined dynamically during initdb.
+      </entry>
+     </row>
+
      <row>
       <entry><literal>EXPLAIN</literal></entry>
       <entry>Parameters with this flag are included in
diff --git a/src/backend/utils/misc/guc_funcs.c b/src/backend/utils/misc/guc_funcs.c
index 108b3bd..2b666e8 100644
--- a/src/backend/utils/misc/guc_funcs.c
+++ b/src/backend/utils/misc/guc_funcs.c
@@ -538,7 +538,7 @@ ShowAllGUCConfig(DestReceiver *dest)
 Datum
 pg_settings_get_flags(PG_FUNCTION_ARGS)
 {
-#define MAX_GUC_FLAGS	6
+#define MAX_GUC_FLAGS	8
 	char	   *varname = TextDatumGetCString(PG_GETARG_DATUM(0));
 	struct config_generic *record;
 	int			cnt = 0;
@@ -551,6 +551,10 @@ pg_settings_get_flags(PG_FUNCTION_ARGS)
 	if (record == NULL)
 		PG_RETURN_NULL();
 
+	if (record->flags & GUC_DEFAULT_COMPILE)
+		flags[cnt++] = CStringGetTextDatum("DEFAULT_COMPILE");
+	if (record->flags & GUC_DEFAULT_INITDB)
+		flags[cnt++] = CStringGetTextDatum("DEFAULT_INITDB");
 	if (record->flags & GUC_EXPLAIN)
 		flags[cnt++] = CStringGetTextDatum("EXPLAIN");
 	if (record->flags & GUC_NO_RESET)
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 05ab087..871be3e 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -600,7 +600,7 @@ StaticAssertDecl(lengthof(GucContext_Names) == (PGC_USERSET + 1),
 const char *const GucSource_Names[] =
 {
 	 /* PGC_S_DEFAULT */ "default",
-	 /* PGC_S_DYNAMIC_DEFAULT */ "default",
+	 /* PGC_S_DYNAMIC_DEFAULT */ "default", //
 	 /* PGC_S_ENV_VAR */ "environment variable",
 	 /* PGC_S_FILE */ "configuration file",
 	 /* PGC_S_ARGV */ "command line",
@@ -1178,7 +1178,7 @@ struct config_bool ConfigureNamesBool[] =
 		{"debug_assertions", PGC_INTERNAL, PRESET_OPTIONS,
 			gettext_noop("Shows whether the running server has assertion checks enabled."),
 			NULL,
-			GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+			GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE | GUC_DEFAULT_COMPILE
 		},
 		&assert_enabled,
 #ifdef USE_ASSERT_CHECKING
@@ -1354,7 +1354,8 @@ struct config_bool ConfigureNamesBool[] =
 	{
 		{"update_process_title", PGC_SUSET, PROCESS_TITLE,
 			gettext_noop("Updates the process title to show the active SQL command."),
-			gettext_noop("Enables updating of the process title every time a new SQL command is received by the server.")
+			gettext_noop("Enables updating of the process title every time a new SQL command is received by the server."),
+			GUC_DEFAULT_COMPILE
 		},
 		&update_process_title,
 #ifdef WIN32
@@ -2103,7 +2104,8 @@ struct config_int ConfigureNamesInt[] =
 	{
 		{"max_connections", PGC_POSTMASTER, CONN_AUTH_SETTINGS,
 			gettext_noop("Sets the maximum number of concurrent connections."),
-			NULL
+			NULL,
+			GUC_DEFAULT_INITDB
 		},
 		&MaxConnections,
 		100, 1, MAX_BACKENDS,
@@ -2140,7 +2142,7 @@ struct config_int ConfigureNamesInt[] =
 		{"shared_buffers", PGC_POSTMASTER, RESOURCES_MEM,
 			gettext_noop("Sets the number of shared memory buffers used by the server."),
 			NULL,
-			GUC_UNIT_BLOCKS
+			GUC_UNIT_BLOCKS | GUC_DEFAULT_INITDB
 		},
 		&NBuffers,
 		16384, 16, INT_MAX / 2,
@@ -2183,7 +2185,8 @@ struct config_int ConfigureNamesInt[] =
 	{
 		{"port", PGC_POSTMASTER, CONN_AUTH_SETTINGS,
 			gettext_noop("Sets the TCP port the server listens on."),
-			NULL
+			NULL,
+			GUC_DEFAULT_COMPILE
 		},
 		&PostPortNumber,
 		DEF_PGPORT, 1, 65535,
@@ -2212,7 +2215,8 @@ struct config_int ConfigureNamesInt[] =
 						 "to be a numeric mode specification in the form "
 						 "accepted by the chmod and umask system calls. "
 						 "(To use the customary octal format the number must "
-						 "start with a 0 (zero).)")
+						 "start with a 0 (zero).)"),
+			GUC_DEFAULT_INITDB
 		},
 		&Log_file_mode,
 		0600, 0000, 0777,
@@ -2654,7 +2658,7 @@ struct config_int ConfigureNamesInt[] =
 		{"checkpoint_flush_after", PGC_SIGHUP, WAL_CHECKPOINTS,
 			gettext_noop("Number of pages after which previously performed writes are flushed to disk."),
 			NULL,
-			GUC_UNIT_BLOCKS
+			GUC_UNIT_BLOCKS | GUC_DEFAULT_COMPILE
 		},
 		&checkpoint_flush_after,
 		DEFAULT_CHECKPOINT_FLUSH_AFTER, 0, WRITEBACK_MAX_PENDING_FLUSHES,
@@ -2872,7 +2876,7 @@ struct config_int ConfigureNamesInt[] =
 		{"bgwriter_flush_after", PGC_SIGHUP, RESOURCES_BGWRITER,
 			gettext_noop("Number of pages after which previously performed writes are flushed to disk."),
 			NULL,
-			GUC_UNIT_BLOCKS
+			GUC_UNIT_BLOCKS | GUC_DEFAULT_COMPILE
 		},
 		&bgwriter_flush_after,
 		DEFAULT_BGWRITER_FLUSH_AFTER, 0, WRITEBACK_MAX_PENDING_FLUSHES,
@@ -2885,7 +2889,7 @@ struct config_int ConfigureNamesInt[] =
 			RESOURCES_ASYNCHRONOUS,
 			gettext_noop("Number of simultaneous requests that can be handled efficiently by the disk subsystem."),
 			NULL,
-			GUC_EXPLAIN
+			GUC_EXPLAIN | GUC_DEFAULT_COMPILE
 		},
 		&effective_io_concurrency,
 #ifdef USE_PREFETCH
@@ -2903,7 +2907,7 @@ struct config_int ConfigureNamesInt[] =
 			RESOURCES_ASYNCHRONOUS,
 			gettext_noop("A variant of effective_io_concurrency that is used for maintenance work."),
 			NULL,
-			GUC_EXPLAIN
+			GUC_EXPLAIN | GUC_DEFAULT_COMPILE
 		},
 		&maintenance_io_concurrency,
 #ifdef USE_PREFETCH
@@ -2920,7 +2924,7 @@ struct config_int ConfigureNamesInt[] =
 		{"backend_flush_after", PGC_USERSET, RESOURCES_ASYNCHRONOUS,
 			gettext_noop("Number of pages after which previously performed writes are flushed to disk."),
 			NULL,
-			GUC_UNIT_BLOCKS
+			GUC_UNIT_BLOCKS | GUC_DEFAULT_COMPILE
 		},
 		&backend_flush_after,
 		DEFAULT_BACKEND_FLUSH_AFTER, 0, WRITEBACK_MAX_PENDING_FLUSHES,
@@ -3363,7 +3367,7 @@ struct config_int ConfigureNamesInt[] =
 		{"debug_discard_caches", PGC_SUSET, DEVELOPER_OPTIONS,
 			gettext_noop("Aggressively flush system caches for debugging purposes."),
 			NULL,
-			GUC_NOT_IN_SAMPLE
+			GUC_NOT_IN_SAMPLE | GUC_DEFAULT_COMPILE
 		},
 		&debug_discard_caches,
 #ifdef DISCARD_CACHES_ENABLED
@@ -3856,7 +3860,8 @@ struct config_string ConfigureNamesString[] =
 	{
 		{"log_timezone", PGC_SIGHUP, LOGGING_WHAT,
 			gettext_noop("Sets the time zone to use in log messages."),
-			NULL
+			NULL,
+			GUC_DEFAULT_INITDB
 		},
 		&log_timezone_string,
 		"GMT",
@@ -3868,7 +3873,7 @@ struct config_string ConfigureNamesString[] =
 			gettext_noop("Sets the display format for date and time values."),
 			gettext_noop("Also controls interpretation of ambiguous "
 						 "date inputs."),
-			GUC_LIST_INPUT | GUC_REPORT
+			GUC_LIST_INPUT | GUC_REPORT | GUC_DEFAULT_INITDB
 		},
 		&datestyle_string,
 		"ISO, MDY",
@@ -3970,7 +3975,8 @@ struct config_string ConfigureNamesString[] =
 	{
 		{"lc_messages", PGC_SUSET, CLIENT_CONN_LOCALE,
 			gettext_noop("Sets the language in which messages are displayed."),
-			NULL
+			NULL,
+			GUC_DEFAULT_INITDB
 		},
 		&locale_messages,
 		"",
@@ -3980,7 +3986,8 @@ struct config_string ConfigureNamesString[] =
 	{
 		{"lc_monetary", PGC_USERSET, CLIENT_CONN_LOCALE,
 			gettext_noop("Sets the locale for formatting monetary amounts."),
-			NULL
+			NULL,
+			GUC_DEFAULT_INITDB
 		},
 		&locale_monetary,
 		"C",
@@ -3990,7 +3997,8 @@ struct config_string ConfigureNamesString[] =
 	{
 		{"lc_numeric", PGC_USERSET, CLIENT_CONN_LOCALE,
 			gettext_noop("Sets the locale for formatting numbers."),
-			NULL
+			NULL,
+			GUC_DEFAULT_INITDB
 		},
 		&locale_numeric,
 		"C",
@@ -4000,7 +4008,8 @@ struct config_string ConfigureNamesString[] =
 	{
 		{"lc_time", PGC_USERSET, CLIENT_CONN_LOCALE,
 			gettext_noop("Sets the locale for formatting date and time values."),
-			NULL
+			NULL,
+			GUC_DEFAULT_INITDB
 		},
 		&locale_time,
 		"C",
@@ -4159,7 +4168,8 @@ struct config_string ConfigureNamesString[] =
 		{"TimeZone", PGC_USERSET, CLIENT_CONN_LOCALE,
 			gettext_noop("Sets the time zone for displaying and interpreting time stamps."),
 			NULL,
-			GUC_REPORT
+			GUC_REPORT | GUC_DEFAULT_INITDB
+
 		},
 		&timezone_string,
 		"GMT",
@@ -4190,7 +4200,7 @@ struct config_string ConfigureNamesString[] =
 		{"unix_socket_directories", PGC_POSTMASTER, CONN_AUTH_SETTINGS,
 			gettext_noop("Sets the directories where Unix-domain sockets will be created."),
 			NULL,
-			GUC_LIST_INPUT | GUC_LIST_QUOTE | GUC_SUPERUSER_ONLY
+			GUC_LIST_INPUT | GUC_LIST_QUOTE | GUC_SUPERUSER_ONLY | GUC_DEFAULT_COMPILE
 		},
 		&Unix_socket_directories,
 		DEFAULT_PGSOCKET_DIR,
@@ -4271,7 +4281,7 @@ struct config_string ConfigureNamesString[] =
 		{"ssl_library", PGC_INTERNAL, PRESET_OPTIONS,
 			gettext_noop("Shows the name of the SSL library."),
 			NULL,
-			GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+			GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE | GUC_DEFAULT_COMPILE
 		},
 		&ssl_library,
 #ifdef USE_SSL
@@ -4346,7 +4356,9 @@ struct config_string ConfigureNamesString[] =
 	{
 		{"default_text_search_config", PGC_USERSET, CLIENT_CONN_LOCALE,
 			gettext_noop("Sets default text search configuration."),
-			NULL
+			NULL,
+			GUC_DEFAULT_INITDB
+
 		},
 		&TSCurrentConfig,
 		"pg_catalog.simple",
@@ -4357,7 +4369,7 @@ struct config_string ConfigureNamesString[] =
 		{"ssl_ciphers", PGC_SIGHUP, CONN_AUTH_SSL,
 			gettext_noop("Sets the list of allowed SSL ciphers."),
 			NULL,
-			GUC_SUPERUSER_ONLY
+			GUC_SUPERUSER_ONLY | GUC_DEFAULT_COMPILE
 		},
 		&SSLCipherSuites,
 #ifdef USE_OPENSSL
@@ -4372,7 +4384,7 @@ struct config_string ConfigureNamesString[] =
 		{"ssl_ecdh_curve", PGC_SIGHUP, CONN_AUTH_SSL,
 			gettext_noop("Sets the curve to use for ECDH."),
 			NULL,
-			GUC_SUPERUSER_ONLY
+			GUC_SUPERUSER_ONLY | GUC_DEFAULT_COMPILE
 		},
 		&SSLECDHCurve,
 #ifdef USE_SSL
@@ -4610,7 +4622,8 @@ struct config_enum ConfigureNamesEnum[] =
 	{
 		{"syslog_facility", PGC_SIGHUP, LOGGING_WHERE,
 			gettext_noop("Sets the syslog \"facility\" to be used when syslog enabled."),
-			NULL
+			NULL,
+			GUC_DEFAULT_COMPILE
 		},
 		&syslog_facility,
 #ifdef HAVE_SYSLOG
@@ -4723,7 +4736,9 @@ struct config_enum ConfigureNamesEnum[] =
 	{
 		{"dynamic_shared_memory_type", PGC_POSTMASTER, RESOURCES_MEM,
 			gettext_noop("Selects the dynamic shared memory implementation used."),
-			NULL
+			NULL,
+			/* platform-specific default, which is also overriden during initdb */
+			GUC_DEFAULT_COMPILE | GUC_DEFAULT_INITDB
 		},
 		&dynamic_shared_memory_type,
 		DEFAULT_DYNAMIC_SHARED_MEMORY_TYPE, dynamic_shared_memory_options,
@@ -4733,7 +4748,8 @@ struct config_enum ConfigureNamesEnum[] =
 	{
 		{"shared_memory_type", PGC_POSTMASTER, RESOURCES_MEM,
 			gettext_noop("Selects the shared memory implementation used for the main shared memory region."),
-			NULL
+			NULL,
+			GUC_DEFAULT_COMPILE
 		},
 		&shared_memory_type,
 		DEFAULT_SHARED_MEMORY_TYPE, shared_memory_options,
@@ -4743,7 +4759,8 @@ struct config_enum ConfigureNamesEnum[] =
 	{
 		{"wal_sync_method", PGC_SIGHUP, WAL_SETTINGS,
 			gettext_noop("Selects the method used for forcing WAL updates to disk."),
-			NULL
+			NULL,
+			GUC_DEFAULT_COMPILE
 		},
 		&sync_method,
 		DEFAULT_SYNC_METHOD, sync_method_options,
@@ -4805,7 +4822,8 @@ struct config_enum ConfigureNamesEnum[] =
 	{
 		{"password_encryption", PGC_USERSET, CONN_AUTH_AUTH,
 			gettext_noop("Chooses the algorithm for encrypting passwords."),
-			NULL
+			NULL,
+			GUC_DEFAULT_INITDB
 		},
 		&Password_encryption,
 		PASSWORD_TYPE_SCRAM_SHA_256, password_encryption_options,
diff --git a/src/include/utils/guc.h b/src/include/utils/guc.h
index b3aaff9..7905358 100644
--- a/src/include/utils/guc.h
+++ b/src/include/utils/guc.h
@@ -221,6 +221,8 @@ typedef enum
 #define GUC_DISALLOW_IN_AUTO_FILE \
 							   0x002000 /* can't set in PG_AUTOCONF_FILENAME */
 #define GUC_RUNTIME_COMPUTED   0x004000 /* delay processing in 'postgres -C' */
+#define GUC_DEFAULT_COMPILE	   0x008000	/* default is determined at compile time */
+#define GUC_DEFAULT_INITDB	   0x010000	/* default is determined at during initdb */
 
 #define GUC_UNIT_KB			 0x01000000 /* value is in kilobytes */
 #define GUC_UNIT_BLOCKS		 0x02000000 /* value is in blocks */
-- 
1.8.3.1

From d8fea6973cec7aad20e9fbb2afe9a19d579bb04b Mon Sep 17 00:00:00 2001
From: Peter Smith <peter.b.smith@fujitsu.com>
Date: Tue, 25 Oct 2022 16:57:32 +1100
Subject: [PATCH v4] GUC C variable sanity check

Added a function to perform a sanity-check comparison of the C variable initial
value with the compiled-in default (boot_val). The purpose of this is to prevent
anybody reading those C declarations from being fooled by mismatched values.

Also fixed some existing mismatching values.

Checking is skipped for GUCs flagged as compiler-dependent (GUC_DEFAULT_COMPILE).
---
 src/backend/access/transam/xact.c   |  2 +-
 src/backend/access/transam/xlog.c   |  2 +-
 src/backend/libpq/be-secure.c       |  4 +-
 src/backend/utils/adt/xml.c         |  4 +-
 src/backend/utils/cache/plancache.c |  2 +-
 src/backend/utils/error/elog.c      |  2 +-
 src/backend/utils/init/globals.c    |  4 +-
 src/backend/utils/misc/guc.c        | 78 +++++++++++++++++++++++++++++++++++++
 src/backend/utils/misc/guc_tables.c |  2 +-
 9 files changed, 89 insertions(+), 11 deletions(-)

diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index fd5103a..f45c95f 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -75,7 +75,7 @@
  *	User-tweakable parameters
  */
 int			DefaultXactIsoLevel = XACT_READ_COMMITTED;
-int			XactIsoLevel;
+int			XactIsoLevel = XACT_READ_COMMITTED;
 
 bool		DefaultXactReadOnly = false;
 bool		XactReadOnly;
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 8f10eff..be54c23 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -131,7 +131,7 @@ bool		wal_init_zero = true;
 bool		wal_recycle = true;
 bool		log_checkpoints = true;
 int			sync_method = DEFAULT_SYNC_METHOD;
-int			wal_level = WAL_LEVEL_MINIMAL;
+int			wal_level = WAL_LEVEL_REPLICA;
 int			CommitDelay = 0;	/* precommit delay in microseconds */
 int			CommitSiblings = 5; /* # concurrent xacts needed to sleep */
 int			wal_retrieve_retry_interval = 5000;
diff --git a/src/backend/libpq/be-secure.c b/src/backend/libpq/be-secure.c
index e3e5471..c896357 100644
--- a/src/backend/libpq/be-secure.c
+++ b/src/backend/libpq/be-secure.c
@@ -58,8 +58,8 @@ char	   *SSLECDHCurve;
 /* GUC variable: if false, prefer client ciphers */
 bool		SSLPreferServerCiphers;
 
-int			ssl_min_protocol_version;
-int			ssl_max_protocol_version;
+int			ssl_min_protocol_version = PG_TLS1_2_VERSION;
+int			ssl_max_protocol_version = PG_TLS_ANY;
 
 /* ------------------------------------------------------------ */
 /*			 Procedures common to all secure sessions			*/
diff --git a/src/backend/utils/adt/xml.c b/src/backend/utils/adt/xml.c
index d32cb11..8cd5262 100644
--- a/src/backend/utils/adt/xml.c
+++ b/src/backend/utils/adt/xml.c
@@ -94,8 +94,8 @@
 
 
 /* GUC variables */
-int			xmlbinary;
-int			xmloption;
+int			xmlbinary = XMLBINARY_BASE64;
+int			xmloption = XMLOPTION_CONTENT;
 
 #ifdef USE_LIBXML
 
diff --git a/src/backend/utils/cache/plancache.c b/src/backend/utils/cache/plancache.c
index 0d6a295..cc94320 100644
--- a/src/backend/utils/cache/plancache.c
+++ b/src/backend/utils/cache/plancache.c
@@ -116,7 +116,7 @@ static void PlanCacheObjectCallback(Datum arg, int cacheid, uint32 hashvalue);
 static void PlanCacheSysCallback(Datum arg, int cacheid, uint32 hashvalue);
 
 /* GUC parameter */
-int			plan_cache_mode;
+int			plan_cache_mode = PLAN_CACHE_MODE_AUTO;
 
 /*
  * InitPlanCache: initialize module during InitPostgres.
diff --git a/src/backend/utils/error/elog.c b/src/backend/utils/error/elog.c
index 6e0a66c..2585e24 100644
--- a/src/backend/utils/error/elog.c
+++ b/src/backend/utils/error/elog.c
@@ -107,7 +107,7 @@ extern bool redirection_done;
 emit_log_hook_type emit_log_hook = NULL;
 
 /* GUC parameters */
-int			Log_error_verbosity = PGERROR_VERBOSE;
+int			Log_error_verbosity = PGERROR_DEFAULT;
 char	   *Log_line_prefix = NULL; /* format for extra log line info */
 int			Log_destination = LOG_DESTINATION_STDERR;
 char	   *Log_destination_string = NULL;
diff --git a/src/backend/utils/init/globals.c b/src/backend/utils/init/globals.c
index 1a5d29a..00bceec 100644
--- a/src/backend/utils/init/globals.c
+++ b/src/backend/utils/init/globals.c
@@ -133,8 +133,8 @@ int			max_parallel_maintenance_workers = 2;
  * MaxBackends is computed by PostmasterMain after modules have had a chance to
  * register background workers.
  */
-int			NBuffers = 1000;
-int			MaxConnections = 90;
+int			NBuffers = 16384;
+int			MaxConnections = 100;
 int			max_worker_processes = 8;
 int			max_parallel_workers = 8;
 int			MaxBackends = 0;
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 6f21752..9e19a3e 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -1382,6 +1382,80 @@ check_GUC_name_for_parameter_acl(const char *name)
 	return false;
 }
 
+#ifdef USE_ASSERT_CHECKING
+/*
+ * A GUC C variable can be declared with an initial value, but the GUC mechanism
+ * will overwrite that using the compiled-in default (boot_val) as per
+ * guc_tables.c.
+ *
+ * This function performs a sanity-check comparison of the C variable initial
+ * value with the boot_val, to prevent anybody reading those C declarations
+ * from being fooled by mismatched values.
+ *
+ * GUC C variable validation rules:
+ * bool - can be false, otherwise must be same as the boot_val
+ * int  - can be 0, otherwise must be same as the boot_val
+ * real - can be 0.0, otherwise must be same as the boot_val
+ * string - can be NULL, otherwise must be strcmp equal to the boot_val
+ * enum - must be same as the boot_val
+ */
+static void
+sanity_check_GUC_C_var(struct config_generic *gconf)
+{
+	/* Skip checking for dynamic (compiler-dependent) GUCs. */
+	if (gconf->flags & GUC_DEFAULT_COMPILE)
+		return;
+
+	switch (gconf->vartype)
+	{
+		case PGC_BOOL:
+			{
+				struct config_bool *conf = (struct config_bool *) gconf;
+
+				if (*conf->variable && !conf->boot_val)
+					elog(FATAL, "GUC (PGC_BOOL) %s, boot_val=%d, C-var=%d",
+						 conf->gen.name, conf->boot_val, *conf->variable);
+				break;
+			}
+		case PGC_INT:
+			{
+				struct config_int *conf = (struct config_int *) gconf;
+
+				if (*conf->variable != 0 && *conf->variable != conf->boot_val)
+					elog(FATAL, "GUC (PGC_INT) %s, boot_val=%d, C-var=%d",
+						 conf->gen.name, conf->boot_val, *conf->variable);
+				break;
+			}
+		case PGC_REAL:
+			{
+				struct config_real *conf = (struct config_real *) gconf;
+
+				if (*conf->variable != 0.0 && *conf->variable != conf->boot_val)
+					elog(FATAL, "GUC (PGC_REAL) %s, boot_val=%g, C-var=%g",
+						 conf->gen.name, conf->boot_val, *conf->variable);
+				break;
+			}
+		case PGC_STRING:
+			{
+				struct config_string *conf = (struct config_string *) gconf;
+
+				if (*conf->variable != NULL && strcmp(*conf->variable, conf->boot_val) != 0)
+					elog(FATAL, "GUC (PGC_STRING) %s, boot_val=%s, C-var=%s",
+						 conf->gen.name, conf->boot_val ? conf->boot_val : "<null>", *conf->variable);
+				break;
+			}
+		case PGC_ENUM:
+			{
+				struct config_enum *conf = (struct config_enum *) gconf;
+
+				if (*conf->variable != conf->boot_val)
+					elog(FATAL, "GUC (PGC_ENUM) %s, boot_val=%d, C-var=%d",
+						 conf->gen.name, conf->boot_val, *conf->variable);
+				break;
+			}
+	}
+}
+#endif
 
 /*
  * Initialize GUC options during program startup.
@@ -1413,6 +1487,10 @@ InitializeGUCOptions(void)
 	hash_seq_init(&status, guc_hashtab);
 	while ((hentry = (GUCHashEntry *) hash_seq_search(&status)) != NULL)
 	{
+#ifdef USE_ASSERT_CHECKING
+		sanity_check_GUC_C_var(hentry->gucvar);
+#endif
+
 		InitializeOneGUCOption(hentry->gucvar);
 	}
 
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 871be3e..0ff2b67 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -526,7 +526,7 @@ int			ssl_renegotiation_limit;
  * This really belongs in pg_shmem.c, but is defined here so that it doesn't
  * need to be duplicated in all the different implementations of pg_shmem.c.
  */
-int			huge_pages;
+int			huge_pages = HUGE_PAGES_TRY;
 int			huge_page_size;
 
 /*
-- 
1.8.3.1

From b3ca1502ede271f68d7db8e8273bee355ce7e0f1 Mon Sep 17 00:00:00 2001
From: Peter Smith <peter.b.smith@fujitsu.com>
Date: Wed, 26 Oct 2022 18:25:08 +1100
Subject: [PATCH v5] GUC C variable sanity check

Added a function to perform a sanity-check comparison of the C variable initial
value with the compiled-in default (boot_val). The purpose of this is to prevent
anybody reading those C declarations from being fooled by mismatched values.

Also fixed some existing mismatching values.
---
 src/backend/access/transam/xact.c   |  2 +-
 src/backend/access/transam/xlog.c   |  2 +-
 src/backend/libpq/be-secure.c       |  4 +--
 src/backend/postmaster/postmaster.c |  2 +-
 src/backend/storage/buffer/bufmgr.c | 20 ++++++++---
 src/backend/storage/ipc/dsm_impl.c  |  2 +-
 src/backend/utils/adt/xml.c         |  4 +--
 src/backend/utils/cache/plancache.c |  2 +-
 src/backend/utils/error/elog.c      |  2 +-
 src/backend/utils/init/globals.c    |  4 +--
 src/backend/utils/misc/guc.c        | 72 +++++++++++++++++++++++++++++++++++++
 src/backend/utils/misc/guc_tables.c | 19 ++++++++--
 src/backend/utils/misc/ps_status.c  |  8 ++++-
 13 files changed, 122 insertions(+), 21 deletions(-)

diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index fd5103a..f45c95f 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -75,7 +75,7 @@
  *	User-tweakable parameters
  */
 int			DefaultXactIsoLevel = XACT_READ_COMMITTED;
-int			XactIsoLevel;
+int			XactIsoLevel = XACT_READ_COMMITTED;
 
 bool		DefaultXactReadOnly = false;
 bool		XactReadOnly;
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 8f10eff..be54c23 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -131,7 +131,7 @@ bool		wal_init_zero = true;
 bool		wal_recycle = true;
 bool		log_checkpoints = true;
 int			sync_method = DEFAULT_SYNC_METHOD;
-int			wal_level = WAL_LEVEL_MINIMAL;
+int			wal_level = WAL_LEVEL_REPLICA;
 int			CommitDelay = 0;	/* precommit delay in microseconds */
 int			CommitSiblings = 5; /* # concurrent xacts needed to sleep */
 int			wal_retrieve_retry_interval = 5000;
diff --git a/src/backend/libpq/be-secure.c b/src/backend/libpq/be-secure.c
index e3e5471..c896357 100644
--- a/src/backend/libpq/be-secure.c
+++ b/src/backend/libpq/be-secure.c
@@ -58,8 +58,8 @@ char	   *SSLECDHCurve;
 /* GUC variable: if false, prefer client ciphers */
 bool		SSLPreferServerCiphers;
 
-int			ssl_min_protocol_version;
-int			ssl_max_protocol_version;
+int			ssl_min_protocol_version = PG_TLS1_2_VERSION;
+int			ssl_max_protocol_version = PG_TLS_ANY;
 
 /* ------------------------------------------------------------ */
 /*			 Procedures common to all secure sessions			*/
diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index 30fb576..0b637ba 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -196,7 +196,7 @@ BackgroundWorker *MyBgworkerEntry = NULL;
 
 
 /* The socket number we are listening for connections on */
-int			PostPortNumber;
+int			PostPortNumber = DEF_PGPORT;
 
 /* The directory names for Unix socket(s) */
 char	   *Unix_socket_directories;
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 6b95381..e5d31e8 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -142,22 +142,32 @@ bool		track_io_timing = false;
  * for buffers not belonging to tablespaces that have their
  * effective_io_concurrency parameter set.
  */
-int			effective_io_concurrency = 0;
+int			effective_io_concurrency =
+#ifdef USE_PREFETCH
+		1;
+#else
+		0;
+#endif
 
 /*
  * Like effective_io_concurrency, but used by maintenance code paths that might
  * benefit from a higher setting because they work on behalf of many sessions.
  * Overridden by the tablespace setting of the same name.
  */
-int			maintenance_io_concurrency = 0;
+int			maintenance_io_concurrency =
+#ifdef USE_PREFETCH
+		10;
+#else
+		0;
+#endif
 
 /*
  * GUC variables about triggering kernel writeback for buffers written; OS
  * dependent defaults are set via the GUC mechanism.
  */
-int			checkpoint_flush_after = 0;
-int			bgwriter_flush_after = 0;
-int			backend_flush_after = 0;
+int			checkpoint_flush_after = DEFAULT_CHECKPOINT_FLUSH_AFTER;
+int			bgwriter_flush_after = DEFAULT_BGWRITER_FLUSH_AFTER;
+int			backend_flush_after = DEFAULT_BACKEND_FLUSH_AFTER;
 
 /* local state for StartBufferIO and related functions */
 static BufferDesc *InProgressBuf = NULL;
diff --git a/src/backend/storage/ipc/dsm_impl.c b/src/backend/storage/ipc/dsm_impl.c
index e1b90c5..6ddd46a 100644
--- a/src/backend/storage/ipc/dsm_impl.c
+++ b/src/backend/storage/ipc/dsm_impl.c
@@ -109,7 +109,7 @@ const struct config_enum_entry dynamic_shared_memory_options[] = {
 };
 
 /* Implementation selector. */
-int			dynamic_shared_memory_type;
+int			dynamic_shared_memory_type = DEFAULT_DYNAMIC_SHARED_MEMORY_TYPE;
 
 /* Amount of space reserved for DSM segments in the main area. */
 int			min_dynamic_shared_memory;
diff --git a/src/backend/utils/adt/xml.c b/src/backend/utils/adt/xml.c
index d32cb11..8cd5262 100644
--- a/src/backend/utils/adt/xml.c
+++ b/src/backend/utils/adt/xml.c
@@ -94,8 +94,8 @@
 
 
 /* GUC variables */
-int			xmlbinary;
-int			xmloption;
+int			xmlbinary = XMLBINARY_BASE64;
+int			xmloption = XMLOPTION_CONTENT;
 
 #ifdef USE_LIBXML
 
diff --git a/src/backend/utils/cache/plancache.c b/src/backend/utils/cache/plancache.c
index 0d6a295..cc94320 100644
--- a/src/backend/utils/cache/plancache.c
+++ b/src/backend/utils/cache/plancache.c
@@ -116,7 +116,7 @@ static void PlanCacheObjectCallback(Datum arg, int cacheid, uint32 hashvalue);
 static void PlanCacheSysCallback(Datum arg, int cacheid, uint32 hashvalue);
 
 /* GUC parameter */
-int			plan_cache_mode;
+int			plan_cache_mode = PLAN_CACHE_MODE_AUTO;
 
 /*
  * InitPlanCache: initialize module during InitPostgres.
diff --git a/src/backend/utils/error/elog.c b/src/backend/utils/error/elog.c
index 6e0a66c..2585e24 100644
--- a/src/backend/utils/error/elog.c
+++ b/src/backend/utils/error/elog.c
@@ -107,7 +107,7 @@ extern bool redirection_done;
 emit_log_hook_type emit_log_hook = NULL;
 
 /* GUC parameters */
-int			Log_error_verbosity = PGERROR_VERBOSE;
+int			Log_error_verbosity = PGERROR_DEFAULT;
 char	   *Log_line_prefix = NULL; /* format for extra log line info */
 int			Log_destination = LOG_DESTINATION_STDERR;
 char	   *Log_destination_string = NULL;
diff --git a/src/backend/utils/init/globals.c b/src/backend/utils/init/globals.c
index 1a5d29a..00bceec 100644
--- a/src/backend/utils/init/globals.c
+++ b/src/backend/utils/init/globals.c
@@ -133,8 +133,8 @@ int			max_parallel_maintenance_workers = 2;
  * MaxBackends is computed by PostmasterMain after modules have had a chance to
  * register background workers.
  */
-int			NBuffers = 1000;
-int			MaxConnections = 90;
+int			NBuffers = 16384;
+int			MaxConnections = 100;
 int			max_worker_processes = 8;
 int			max_parallel_workers = 8;
 int			MaxBackends = 0;
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 6f21752..7c9c4be 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -1382,6 +1382,77 @@ check_GUC_name_for_parameter_acl(const char *name)
 	return false;
 }
 
+/*
+ * A GUC C variable can be declared with an initial value, but the GUC mechanism
+ * will overwrite that using the compiled-in default (boot_val) as per
+ * guc_tables.c.
+ *
+ * This function performs a sanity-check comparison of the C variable initial
+ * value with the boot_val, to prevent anybody reading those C declarations
+ * from being fooled by mismatched values.
+ *
+ * GUC C variable validation rules:
+ * bool - can be false, otherwise must be same as the boot_val
+ * int  - can be 0, otherwise must be same as the boot_val
+ * real - can be 0.0, otherwise must be same as the boot_val
+ * string - can be NULL, otherwise must be strcmp equal to the boot_val
+ * enum - must be same as the boot_val
+ */
+static void
+sanity_check_GUC_C_var(struct config_generic *gconf)
+{
+#ifdef USE_ASSERT_CHECKING
+
+	switch (gconf->vartype)
+	{
+		case PGC_BOOL:
+			{
+				struct config_bool *conf = (struct config_bool *) gconf;
+
+				if (*conf->variable && !conf->boot_val)
+					elog(FATAL, "GUC (PGC_BOOL) %s, boot_val=%d, C-var=%d",
+						 conf->gen.name, conf->boot_val, *conf->variable);
+				break;
+			}
+		case PGC_INT:
+			{
+				struct config_int *conf = (struct config_int *) gconf;
+
+				if (*conf->variable != 0 && *conf->variable != conf->boot_val)
+					elog(FATAL, "GUC (PGC_INT) %s, boot_val=%d, C-var=%d",
+						 conf->gen.name, conf->boot_val, *conf->variable);
+				break;
+			}
+		case PGC_REAL:
+			{
+				struct config_real *conf = (struct config_real *) gconf;
+
+				if (*conf->variable != 0.0 && *conf->variable != conf->boot_val)
+					elog(FATAL, "GUC (PGC_REAL) %s, boot_val=%g, C-var=%g",
+						 conf->gen.name, conf->boot_val, *conf->variable);
+				break;
+			}
+		case PGC_STRING:
+			{
+				struct config_string *conf = (struct config_string *) gconf;
+
+				if (*conf->variable != NULL && strcmp(*conf->variable, conf->boot_val) != 0)
+					elog(FATAL, "GUC (PGC_STRING) %s, boot_val=%s, C-var=%s",
+						 conf->gen.name, conf->boot_val ? conf->boot_val : "<null>", *conf->variable);
+				break;
+			}
+		case PGC_ENUM:
+			{
+				struct config_enum *conf = (struct config_enum *) gconf;
+
+				if (*conf->variable != conf->boot_val)
+					elog(FATAL, "GUC (PGC_ENUM) %s, boot_val=%d, C-var=%d",
+						 conf->gen.name, conf->boot_val, *conf->variable);
+				break;
+			}
+	}
+#endif
+}
 
 /*
  * Initialize GUC options during program startup.
@@ -1413,6 +1484,7 @@ InitializeGUCOptions(void)
 	hash_seq_init(&status, guc_hashtab);
 	while ((hentry = (GUCHashEntry *) hash_seq_search(&status)) != NULL)
 	{
+		sanity_check_GUC_C_var(hentry->gucvar);
 		InitializeOneGUCOption(hentry->gucvar);
 	}
 
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 05ab087..da387f1 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -526,13 +526,16 @@ int			ssl_renegotiation_limit;
  * This really belongs in pg_shmem.c, but is defined here so that it doesn't
  * need to be duplicated in all the different implementations of pg_shmem.c.
  */
-int			huge_pages;
+int			huge_pages = HUGE_PAGES_TRY;
 int			huge_page_size;
 
 /*
  * These variables are all dummies that don't do anything, except in some
  * cases provide the value for SHOW to display.  The real state is elsewhere
  * and is kept in sync by assign_hooks.
+ *
+ * Declaration assignments here are for keeping the GUC C var sanity-checker
+ * happy.
  */
 static char *syslog_ident_str;
 static double phony_random_seed;
@@ -543,7 +546,12 @@ static char *locale_ctype;
 static char *server_encoding_string;
 static char *server_version_string;
 static int	server_version_num;
-static int	syslog_facility;
+static int	syslog_facility =
+#ifdef HAVE_SYSLOG
+		LOG_LOCAL0;
+#else
+		0;
+#endif
 static char *timezone_string;
 static char *log_timezone_string;
 static char *timezone_abbreviations_string;
@@ -559,7 +567,12 @@ static int	shared_memory_size_in_huge_pages;
 static int	wal_block_size;
 static bool data_checksums;
 static bool integer_datetimes;
-static bool assert_enabled;
+static bool assert_enabled =
+#ifdef USE_ASSERT_CHECKING
+		true;
+#else
+		false;
+#endif
 static char *recovery_target_timeline_string;
 static char *recovery_target_string;
 static char *recovery_target_xid_string;
diff --git a/src/backend/utils/misc/ps_status.c b/src/backend/utils/misc/ps_status.c
index 8520ce7..46ade41 100644
--- a/src/backend/utils/misc/ps_status.c
+++ b/src/backend/utils/misc/ps_status.c
@@ -30,8 +30,14 @@
 #include "utils/ps_status.h"
 
 extern char **environ;
-bool		update_process_title = true;
 
+/* GUC variable */
+bool		update_process_title =
+#ifdef WIN32
+		false;
+#else
+		true;
+#endif
 
 /*
  * Alternative ways of updating ps display:
-- 
1.8.3.1

From cfc89f2e5b418a64c30a5b6e88aee8e27769c71b Mon Sep 17 00:00:00 2001
From: Peter Smith <peter.b.smith@fujitsu.com>
Date: Thu, 27 Oct 2022 18:45:34 +1100
Subject: [PATCH v6] GUC C variable sanity check

Added a function to perform a sanity-check comparison of the C variable initial
value with the compiled-in default (boot_val). The purpose of this is to prevent
anybody reading those C declarations from being fooled by mismatched values.

Also fixed some existing mismatching values.
---
 src/backend/access/transam/xact.c   |  2 +-
 src/backend/access/transam/xlog.c   |  2 +-
 src/backend/libpq/be-secure.c       |  4 +--
 src/backend/postmaster/postmaster.c |  2 +-
 src/backend/storage/buffer/bufmgr.c | 10 +++---
 src/backend/storage/ipc/dsm_impl.c  |  2 +-
 src/backend/utils/adt/xml.c         |  4 +--
 src/backend/utils/cache/plancache.c |  2 +-
 src/backend/utils/error/elog.c      |  2 +-
 src/backend/utils/init/globals.c    |  4 +--
 src/backend/utils/misc/guc.c        | 72 +++++++++++++++++++++++++++++++++++++
 src/backend/utils/misc/guc_tables.c | 53 +++++++++++++--------------
 src/backend/utils/misc/ps_status.c  |  3 +-
 src/include/storage/bufmgr.h        |  8 +++++
 src/include/utils/ps_status.h       |  5 +++
 15 files changed, 129 insertions(+), 46 deletions(-)

diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index fd5103a..f45c95f 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -75,7 +75,7 @@
  *	User-tweakable parameters
  */
 int			DefaultXactIsoLevel = XACT_READ_COMMITTED;
-int			XactIsoLevel;
+int			XactIsoLevel = XACT_READ_COMMITTED;
 
 bool		DefaultXactReadOnly = false;
 bool		XactReadOnly;
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 8f10eff..be54c23 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -131,7 +131,7 @@ bool		wal_init_zero = true;
 bool		wal_recycle = true;
 bool		log_checkpoints = true;
 int			sync_method = DEFAULT_SYNC_METHOD;
-int			wal_level = WAL_LEVEL_MINIMAL;
+int			wal_level = WAL_LEVEL_REPLICA;
 int			CommitDelay = 0;	/* precommit delay in microseconds */
 int			CommitSiblings = 5; /* # concurrent xacts needed to sleep */
 int			wal_retrieve_retry_interval = 5000;
diff --git a/src/backend/libpq/be-secure.c b/src/backend/libpq/be-secure.c
index e3e5471..c896357 100644
--- a/src/backend/libpq/be-secure.c
+++ b/src/backend/libpq/be-secure.c
@@ -58,8 +58,8 @@ char	   *SSLECDHCurve;
 /* GUC variable: if false, prefer client ciphers */
 bool		SSLPreferServerCiphers;
 
-int			ssl_min_protocol_version;
-int			ssl_max_protocol_version;
+int			ssl_min_protocol_version = PG_TLS1_2_VERSION;
+int			ssl_max_protocol_version = PG_TLS_ANY;
 
 /* ------------------------------------------------------------ */
 /*			 Procedures common to all secure sessions			*/
diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index 30fb576..0b637ba 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -196,7 +196,7 @@ BackgroundWorker *MyBgworkerEntry = NULL;
 
 
 /* The socket number we are listening for connections on */
-int			PostPortNumber;
+int			PostPortNumber = DEF_PGPORT;
 
 /* The directory names for Unix socket(s) */
 char	   *Unix_socket_directories;
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 6b95381..73d30bf 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -142,22 +142,22 @@ bool		track_io_timing = false;
  * for buffers not belonging to tablespaces that have their
  * effective_io_concurrency parameter set.
  */
-int			effective_io_concurrency = 0;
+int			effective_io_concurrency = DEFAULT_EFFECTIVE_IO_CONCURRENCY;
 
 /*
  * Like effective_io_concurrency, but used by maintenance code paths that might
  * benefit from a higher setting because they work on behalf of many sessions.
  * Overridden by the tablespace setting of the same name.
  */
-int			maintenance_io_concurrency = 0;
+int			maintenance_io_concurrency = DEFAULT_MAINTENANCE_IO_CONCURRENCY;
 
 /*
  * GUC variables about triggering kernel writeback for buffers written; OS
  * dependent defaults are set via the GUC mechanism.
  */
-int			checkpoint_flush_after = 0;
-int			bgwriter_flush_after = 0;
-int			backend_flush_after = 0;
+int			checkpoint_flush_after = DEFAULT_CHECKPOINT_FLUSH_AFTER;
+int			bgwriter_flush_after = DEFAULT_BGWRITER_FLUSH_AFTER;
+int			backend_flush_after = DEFAULT_BACKEND_FLUSH_AFTER;
 
 /* local state for StartBufferIO and related functions */
 static BufferDesc *InProgressBuf = NULL;
diff --git a/src/backend/storage/ipc/dsm_impl.c b/src/backend/storage/ipc/dsm_impl.c
index e1b90c5..6ddd46a 100644
--- a/src/backend/storage/ipc/dsm_impl.c
+++ b/src/backend/storage/ipc/dsm_impl.c
@@ -109,7 +109,7 @@ const struct config_enum_entry dynamic_shared_memory_options[] = {
 };
 
 /* Implementation selector. */
-int			dynamic_shared_memory_type;
+int			dynamic_shared_memory_type = DEFAULT_DYNAMIC_SHARED_MEMORY_TYPE;
 
 /* Amount of space reserved for DSM segments in the main area. */
 int			min_dynamic_shared_memory;
diff --git a/src/backend/utils/adt/xml.c b/src/backend/utils/adt/xml.c
index d32cb11..8cd5262 100644
--- a/src/backend/utils/adt/xml.c
+++ b/src/backend/utils/adt/xml.c
@@ -94,8 +94,8 @@
 
 
 /* GUC variables */
-int			xmlbinary;
-int			xmloption;
+int			xmlbinary = XMLBINARY_BASE64;
+int			xmloption = XMLOPTION_CONTENT;
 
 #ifdef USE_LIBXML
 
diff --git a/src/backend/utils/cache/plancache.c b/src/backend/utils/cache/plancache.c
index 0d6a295..cc94320 100644
--- a/src/backend/utils/cache/plancache.c
+++ b/src/backend/utils/cache/plancache.c
@@ -116,7 +116,7 @@ static void PlanCacheObjectCallback(Datum arg, int cacheid, uint32 hashvalue);
 static void PlanCacheSysCallback(Datum arg, int cacheid, uint32 hashvalue);
 
 /* GUC parameter */
-int			plan_cache_mode;
+int			plan_cache_mode = PLAN_CACHE_MODE_AUTO;
 
 /*
  * InitPlanCache: initialize module during InitPostgres.
diff --git a/src/backend/utils/error/elog.c b/src/backend/utils/error/elog.c
index 6e0a66c..2585e24 100644
--- a/src/backend/utils/error/elog.c
+++ b/src/backend/utils/error/elog.c
@@ -107,7 +107,7 @@ extern bool redirection_done;
 emit_log_hook_type emit_log_hook = NULL;
 
 /* GUC parameters */
-int			Log_error_verbosity = PGERROR_VERBOSE;
+int			Log_error_verbosity = PGERROR_DEFAULT;
 char	   *Log_line_prefix = NULL; /* format for extra log line info */
 int			Log_destination = LOG_DESTINATION_STDERR;
 char	   *Log_destination_string = NULL;
diff --git a/src/backend/utils/init/globals.c b/src/backend/utils/init/globals.c
index 1a5d29a..00bceec 100644
--- a/src/backend/utils/init/globals.c
+++ b/src/backend/utils/init/globals.c
@@ -133,8 +133,8 @@ int			max_parallel_maintenance_workers = 2;
  * MaxBackends is computed by PostmasterMain after modules have had a chance to
  * register background workers.
  */
-int			NBuffers = 1000;
-int			MaxConnections = 90;
+int			NBuffers = 16384;
+int			MaxConnections = 100;
 int			max_worker_processes = 8;
 int			max_parallel_workers = 8;
 int			MaxBackends = 0;
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 6f21752..7c9c4be 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -1382,6 +1382,77 @@ check_GUC_name_for_parameter_acl(const char *name)
 	return false;
 }
 
+/*
+ * A GUC C variable can be declared with an initial value, but the GUC mechanism
+ * will overwrite that using the compiled-in default (boot_val) as per
+ * guc_tables.c.
+ *
+ * This function performs a sanity-check comparison of the C variable initial
+ * value with the boot_val, to prevent anybody reading those C declarations
+ * from being fooled by mismatched values.
+ *
+ * GUC C variable validation rules:
+ * bool - can be false, otherwise must be same as the boot_val
+ * int  - can be 0, otherwise must be same as the boot_val
+ * real - can be 0.0, otherwise must be same as the boot_val
+ * string - can be NULL, otherwise must be strcmp equal to the boot_val
+ * enum - must be same as the boot_val
+ */
+static void
+sanity_check_GUC_C_var(struct config_generic *gconf)
+{
+#ifdef USE_ASSERT_CHECKING
+
+	switch (gconf->vartype)
+	{
+		case PGC_BOOL:
+			{
+				struct config_bool *conf = (struct config_bool *) gconf;
+
+				if (*conf->variable && !conf->boot_val)
+					elog(FATAL, "GUC (PGC_BOOL) %s, boot_val=%d, C-var=%d",
+						 conf->gen.name, conf->boot_val, *conf->variable);
+				break;
+			}
+		case PGC_INT:
+			{
+				struct config_int *conf = (struct config_int *) gconf;
+
+				if (*conf->variable != 0 && *conf->variable != conf->boot_val)
+					elog(FATAL, "GUC (PGC_INT) %s, boot_val=%d, C-var=%d",
+						 conf->gen.name, conf->boot_val, *conf->variable);
+				break;
+			}
+		case PGC_REAL:
+			{
+				struct config_real *conf = (struct config_real *) gconf;
+
+				if (*conf->variable != 0.0 && *conf->variable != conf->boot_val)
+					elog(FATAL, "GUC (PGC_REAL) %s, boot_val=%g, C-var=%g",
+						 conf->gen.name, conf->boot_val, *conf->variable);
+				break;
+			}
+		case PGC_STRING:
+			{
+				struct config_string *conf = (struct config_string *) gconf;
+
+				if (*conf->variable != NULL && strcmp(*conf->variable, conf->boot_val) != 0)
+					elog(FATAL, "GUC (PGC_STRING) %s, boot_val=%s, C-var=%s",
+						 conf->gen.name, conf->boot_val ? conf->boot_val : "<null>", *conf->variable);
+				break;
+			}
+		case PGC_ENUM:
+			{
+				struct config_enum *conf = (struct config_enum *) gconf;
+
+				if (*conf->variable != conf->boot_val)
+					elog(FATAL, "GUC (PGC_ENUM) %s, boot_val=%d, C-var=%d",
+						 conf->gen.name, conf->boot_val, *conf->variable);
+				break;
+			}
+	}
+#endif
+}
 
 /*
  * Initialize GUC options during program startup.
@@ -1413,6 +1484,7 @@ InitializeGUCOptions(void)
 	hash_seq_init(&status, guc_hashtab);
 	while ((hentry = (GUCHashEntry *) hash_seq_search(&status)) != NULL)
 	{
+		sanity_check_GUC_C_var(hentry->gucvar);
 		InitializeOneGUCOption(hentry->gucvar);
 	}
 
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 05ab087..9fd1674 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -526,13 +526,16 @@ int			ssl_renegotiation_limit;
  * This really belongs in pg_shmem.c, but is defined here so that it doesn't
  * need to be duplicated in all the different implementations of pg_shmem.c.
  */
-int			huge_pages;
+int			huge_pages = HUGE_PAGES_TRY;
 int			huge_page_size;
 
 /*
  * These variables are all dummies that don't do anything, except in some
  * cases provide the value for SHOW to display.  The real state is elsewhere
  * and is kept in sync by assign_hooks.
+ *
+ * Declaration assignments here are for keeping the GUC C var sanity-checker
+ * happy.
  */
 static char *syslog_ident_str;
 static double phony_random_seed;
@@ -543,7 +546,14 @@ static char *locale_ctype;
 static char *server_encoding_string;
 static char *server_version_string;
 static int	server_version_num;
-static int	syslog_facility;
+
+#ifdef HAVE_SYSLOG
+#define	DEFAULT_SYSLOG_FACILITY LOG_LOCAL0
+#else
+#define	DEFAULT_SYSLOG_FACILITY 0
+#endif
+static int	syslog_facility = DEFAULT_SYSLOG_FACILITY;
+
 static char *timezone_string;
 static char *log_timezone_string;
 static char *timezone_abbreviations_string;
@@ -559,7 +569,14 @@ static int	shared_memory_size_in_huge_pages;
 static int	wal_block_size;
 static bool data_checksums;
 static bool integer_datetimes;
-static bool assert_enabled;
+
+#ifdef USE_ASSERT_CHECKING
+#define DEFAULT_ASSERT_ENABLED true
+#else
+#define DEFAULT_ASSERT_ENABLED false
+#endif
+static bool assert_enabled = DEFAULT_ASSERT_ENABLED;
+
 static char *recovery_target_timeline_string;
 static char *recovery_target_string;
 static char *recovery_target_xid_string;
@@ -1181,11 +1198,7 @@ struct config_bool ConfigureNamesBool[] =
 			GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
 		},
 		&assert_enabled,
-#ifdef USE_ASSERT_CHECKING
-		true,
-#else
-		false,
-#endif
+		DEFAULT_ASSERT_ENABLED,
 		NULL, NULL, NULL
 	},
 
@@ -1357,11 +1370,7 @@ struct config_bool ConfigureNamesBool[] =
 			gettext_noop("Enables updating of the process title every time a new SQL command is received by the server.")
 		},
 		&update_process_title,
-#ifdef WIN32
-		false,
-#else
-		true,
-#endif
+		DEFAULT_UPDATE_PROCESS_TITLE,
 		NULL, NULL, NULL
 	},
 
@@ -2888,11 +2897,7 @@ struct config_int ConfigureNamesInt[] =
 			GUC_EXPLAIN
 		},
 		&effective_io_concurrency,
-#ifdef USE_PREFETCH
-		1,
-#else
-		0,
-#endif
+		DEFAULT_EFFECTIVE_IO_CONCURRENCY,
 		0, MAX_IO_CONCURRENCY,
 		check_effective_io_concurrency, NULL, NULL
 	},
@@ -2906,11 +2911,7 @@ struct config_int ConfigureNamesInt[] =
 			GUC_EXPLAIN
 		},
 		&maintenance_io_concurrency,
-#ifdef USE_PREFETCH
-		10,
-#else
-		0,
-#endif
+		DEFAULT_MAINTENANCE_IO_CONCURRENCY,
 		0, MAX_IO_CONCURRENCY,
 		check_maintenance_io_concurrency, assign_maintenance_io_concurrency,
 		NULL
@@ -4613,11 +4614,7 @@ struct config_enum ConfigureNamesEnum[] =
 			NULL
 		},
 		&syslog_facility,
-#ifdef HAVE_SYSLOG
-		LOG_LOCAL0,
-#else
-		0,
-#endif
+		DEFAULT_SYSLOG_FACILITY,
 		syslog_facility_options,
 		NULL, assign_syslog_facility, NULL
 	},
diff --git a/src/backend/utils/misc/ps_status.c b/src/backend/utils/misc/ps_status.c
index 8520ce7..d81a67b 100644
--- a/src/backend/utils/misc/ps_status.c
+++ b/src/backend/utils/misc/ps_status.c
@@ -30,8 +30,9 @@
 #include "utils/ps_status.h"
 
 extern char **environ;
-bool		update_process_title = true;
 
+/* GUC variable */
+bool		update_process_title = DEFAULT_UPDATE_PROCESS_TITLE;
 
 /*
  * Alternative ways of updating ps display:
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 6f4dfa0..185c3b9 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -69,6 +69,14 @@ extern PGDLLIMPORT bool zero_damaged_pages;
 extern PGDLLIMPORT int bgwriter_lru_maxpages;
 extern PGDLLIMPORT double bgwriter_lru_multiplier;
 extern PGDLLIMPORT bool track_io_timing;
+
+#ifdef USE_PREFETCH
+#define DEFAULT_EFFECTIVE_IO_CONCURRENCY 1
+#define DEFAULT_MAINTENANCE_IO_CONCURRENCY 10
+#else
+#define DEFAULT_EFFECTIVE_IO_CONCURRENCY 0
+#define DEFAULT_MAINTENANCE_IO_CONCURRENCY 0
+#endif
 extern PGDLLIMPORT int effective_io_concurrency;
 extern PGDLLIMPORT int maintenance_io_concurrency;
 
diff --git a/src/include/utils/ps_status.h b/src/include/utils/ps_status.h
index bba4635..3e9e98d 100644
--- a/src/include/utils/ps_status.h
+++ b/src/include/utils/ps_status.h
@@ -12,6 +12,11 @@
 #ifndef PS_STATUS_H
 #define PS_STATUS_H
 
+#ifdef WIN32
+#define DEFAULT_UPDATE_PROCESS_TITLE false
+#else
+#define DEFAULT_UPDATE_PROCESS_TITLE true
+#endif
 extern PGDLLIMPORT bool update_process_title;
 
 extern char **save_ps_display_args(int argc, char **argv);
-- 
1.8.3.1

From 3f742d6433d88895720f6801c59213f0f4ad17f9 Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Fri, 28 Oct 2022 16:03:08 +0900
Subject: [PATCH v7] GUC C variable sanity check

Added a function to perform a sanity-check comparison of the C variable initial
value with the compiled-in default (boot_val). The purpose of this is to prevent
anybody reading those C declarations from being fooled by mismatched values.

Also fixed some existing mismatching values.
---
 src/include/storage/bufmgr.h                  |  9 ++
 src/include/utils/ps_status.h                 |  6 ++
 src/backend/access/transam/xact.c             |  2 +-
 src/backend/access/transam/xlog.c             |  2 +-
 src/backend/libpq/be-secure.c                 |  4 +-
 src/backend/postmaster/postmaster.c           |  2 +-
 src/backend/storage/buffer/bufmgr.c           | 10 +--
 src/backend/storage/ipc/dsm_impl.c            |  2 +-
 src/backend/utils/adt/xml.c                   |  4 +-
 src/backend/utils/cache/plancache.c           |  2 +-
 src/backend/utils/error/elog.c                |  2 +-
 src/backend/utils/init/globals.c              |  4 +-
 src/backend/utils/misc/guc.c                  | 89 +++++++++++++++++++
 src/backend/utils/misc/guc_tables.c           | 50 +++++------
 src/backend/utils/misc/ps_status.c            |  3 +-
 contrib/auth_delay/auth_delay.c               |  2 +-
 contrib/pg_prewarm/autoprewarm.c              |  2 +-
 .../pg_stat_statements/pg_stat_statements.c   | 10 +--
 contrib/pg_trgm/trgm_op.c                     |  6 +-
 contrib/sepgsql/hooks.c                       |  4 +-
 20 files changed, 157 insertions(+), 58 deletions(-)

diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 6f4dfa0960..a1e933f62e 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -69,6 +69,15 @@ extern PGDLLIMPORT bool zero_damaged_pages;
 extern PGDLLIMPORT int bgwriter_lru_maxpages;
 extern PGDLLIMPORT double bgwriter_lru_multiplier;
 extern PGDLLIMPORT bool track_io_timing;
+
+/* effective when prefetching is available */
+#ifdef USE_PREFETCH
+#define DEFAULT_EFFECTIVE_IO_CONCURRENCY 1
+#define DEFAULT_MAINTENANCE_IO_CONCURRENCY 10
+#else
+#define DEFAULT_EFFECTIVE_IO_CONCURRENCY 0
+#define DEFAULT_MAINTENANCE_IO_CONCURRENCY 0
+#endif
 extern PGDLLIMPORT int effective_io_concurrency;
 extern PGDLLIMPORT int maintenance_io_concurrency;
 
diff --git a/src/include/utils/ps_status.h b/src/include/utils/ps_status.h
index bba463591f..3bf212e3fd 100644
--- a/src/include/utils/ps_status.h
+++ b/src/include/utils/ps_status.h
@@ -12,6 +12,12 @@
 #ifndef PS_STATUS_H
 #define PS_STATUS_H
 
+/* Disabled on Windows as the performance overhead can be significant */
+#ifdef WIN32
+#define DEFAULT_UPDATE_PROCESS_TITLE false
+#else
+#define DEFAULT_UPDATE_PROCESS_TITLE true
+#endif
 extern PGDLLIMPORT bool update_process_title;
 
 extern char **save_ps_display_args(int argc, char **argv);
diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index fd5103a78e..f45c95faf6 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -75,7 +75,7 @@
  *	User-tweakable parameters
  */
 int			DefaultXactIsoLevel = XACT_READ_COMMITTED;
-int			XactIsoLevel;
+int			XactIsoLevel = XACT_READ_COMMITTED;
 
 bool		DefaultXactReadOnly = false;
 bool		XactReadOnly;
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 8f10effe3a..be54c23187 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -131,7 +131,7 @@ bool		wal_init_zero = true;
 bool		wal_recycle = true;
 bool		log_checkpoints = true;
 int			sync_method = DEFAULT_SYNC_METHOD;
-int			wal_level = WAL_LEVEL_MINIMAL;
+int			wal_level = WAL_LEVEL_REPLICA;
 int			CommitDelay = 0;	/* precommit delay in microseconds */
 int			CommitSiblings = 5; /* # concurrent xacts needed to sleep */
 int			wal_retrieve_retry_interval = 5000;
diff --git a/src/backend/libpq/be-secure.c b/src/backend/libpq/be-secure.c
index e3e54713e8..c8963572a7 100644
--- a/src/backend/libpq/be-secure.c
+++ b/src/backend/libpq/be-secure.c
@@ -58,8 +58,8 @@ char	   *SSLECDHCurve;
 /* GUC variable: if false, prefer client ciphers */
 bool		SSLPreferServerCiphers;
 
-int			ssl_min_protocol_version;
-int			ssl_max_protocol_version;
+int			ssl_min_protocol_version = PG_TLS1_2_VERSION;
+int			ssl_max_protocol_version = PG_TLS_ANY;
 
 /* ------------------------------------------------------------ */
 /*			 Procedures common to all secure sessions			*/
diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index 30fb576ac3..0b637ba6a2 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -196,7 +196,7 @@ BackgroundWorker *MyBgworkerEntry = NULL;
 
 
 /* The socket number we are listening for connections on */
-int			PostPortNumber;
+int			PostPortNumber = DEF_PGPORT;
 
 /* The directory names for Unix socket(s) */
 char	   *Unix_socket_directories;
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 6b95381481..73d30bf619 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -142,22 +142,22 @@ bool		track_io_timing = false;
  * for buffers not belonging to tablespaces that have their
  * effective_io_concurrency parameter set.
  */
-int			effective_io_concurrency = 0;
+int			effective_io_concurrency = DEFAULT_EFFECTIVE_IO_CONCURRENCY;
 
 /*
  * Like effective_io_concurrency, but used by maintenance code paths that might
  * benefit from a higher setting because they work on behalf of many sessions.
  * Overridden by the tablespace setting of the same name.
  */
-int			maintenance_io_concurrency = 0;
+int			maintenance_io_concurrency = DEFAULT_MAINTENANCE_IO_CONCURRENCY;
 
 /*
  * GUC variables about triggering kernel writeback for buffers written; OS
  * dependent defaults are set via the GUC mechanism.
  */
-int			checkpoint_flush_after = 0;
-int			bgwriter_flush_after = 0;
-int			backend_flush_after = 0;
+int			checkpoint_flush_after = DEFAULT_CHECKPOINT_FLUSH_AFTER;
+int			bgwriter_flush_after = DEFAULT_BGWRITER_FLUSH_AFTER;
+int			backend_flush_after = DEFAULT_BACKEND_FLUSH_AFTER;
 
 /* local state for StartBufferIO and related functions */
 static BufferDesc *InProgressBuf = NULL;
diff --git a/src/backend/storage/ipc/dsm_impl.c b/src/backend/storage/ipc/dsm_impl.c
index e1b90c5de4..6ddd46a4e7 100644
--- a/src/backend/storage/ipc/dsm_impl.c
+++ b/src/backend/storage/ipc/dsm_impl.c
@@ -109,7 +109,7 @@ const struct config_enum_entry dynamic_shared_memory_options[] = {
 };
 
 /* Implementation selector. */
-int			dynamic_shared_memory_type;
+int			dynamic_shared_memory_type = DEFAULT_DYNAMIC_SHARED_MEMORY_TYPE;
 
 /* Amount of space reserved for DSM segments in the main area. */
 int			min_dynamic_shared_memory;
diff --git a/src/backend/utils/adt/xml.c b/src/backend/utils/adt/xml.c
index d32cb11436..8cd5262a3c 100644
--- a/src/backend/utils/adt/xml.c
+++ b/src/backend/utils/adt/xml.c
@@ -94,8 +94,8 @@
 
 
 /* GUC variables */
-int			xmlbinary;
-int			xmloption;
+int			xmlbinary = XMLBINARY_BASE64;
+int			xmloption = XMLOPTION_CONTENT;
 
 #ifdef USE_LIBXML
 
diff --git a/src/backend/utils/cache/plancache.c b/src/backend/utils/cache/plancache.c
index 0d6a295674..cc943205d3 100644
--- a/src/backend/utils/cache/plancache.c
+++ b/src/backend/utils/cache/plancache.c
@@ -116,7 +116,7 @@ static void PlanCacheObjectCallback(Datum arg, int cacheid, uint32 hashvalue);
 static void PlanCacheSysCallback(Datum arg, int cacheid, uint32 hashvalue);
 
 /* GUC parameter */
-int			plan_cache_mode;
+int			plan_cache_mode = PLAN_CACHE_MODE_AUTO;
 
 /*
  * InitPlanCache: initialize module during InitPostgres.
diff --git a/src/backend/utils/error/elog.c b/src/backend/utils/error/elog.c
index 6e0a66c29e..2585e24845 100644
--- a/src/backend/utils/error/elog.c
+++ b/src/backend/utils/error/elog.c
@@ -107,7 +107,7 @@ extern bool redirection_done;
 emit_log_hook_type emit_log_hook = NULL;
 
 /* GUC parameters */
-int			Log_error_verbosity = PGERROR_VERBOSE;
+int			Log_error_verbosity = PGERROR_DEFAULT;
 char	   *Log_line_prefix = NULL; /* format for extra log line info */
 int			Log_destination = LOG_DESTINATION_STDERR;
 char	   *Log_destination_string = NULL;
diff --git a/src/backend/utils/init/globals.c b/src/backend/utils/init/globals.c
index 1a5d29ac9b..00bceec8fa 100644
--- a/src/backend/utils/init/globals.c
+++ b/src/backend/utils/init/globals.c
@@ -133,8 +133,8 @@ int			max_parallel_maintenance_workers = 2;
  * MaxBackends is computed by PostmasterMain after modules have had a chance to
  * register background workers.
  */
-int			NBuffers = 1000;
-int			MaxConnections = 90;
+int			NBuffers = 16384;
+int			MaxConnections = 100;
 int			max_worker_processes = 8;
 int			max_parallel_workers = 8;
 int			MaxBackends = 0;
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 6f21752b84..6657f0d92e 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -1382,6 +1382,89 @@ check_GUC_name_for_parameter_acl(const char *name)
 	return false;
 }
 
+/*
+ * Routine in charge of checking that the initial value of a GUC is the
+ * same when declared and when loaded to prevent anybody looking at the
+ * C declarations of these GUCS from being fooled by mismatched values.
+ *
+ * The following validation rules apply:
+ * bool - can be false, otherwise must be same as the boot_val
+ * int  - can be 0, otherwise must be same as the boot_val
+ * real - can be 0.0, otherwise must be same as the boot_val
+ * string - can be NULL, otherwise must be strcmp equal to the boot_val
+ * enum - must be same as the boot_val
+ */
+#ifdef USE_ASSERT_CHECKING
+static bool
+check_GUC_init(struct config_generic *gconf)
+{
+	switch (gconf->vartype)
+	{
+		case PGC_BOOL:
+			{
+				struct config_bool *conf = (struct config_bool *) gconf;
+
+				if (*conf->variable && !conf->boot_val)
+				{
+					elog(LOG, "GUC (PGC_BOOL) %s, boot_val=%d, C-var=%d",
+						 conf->gen.name, conf->boot_val, *conf->variable);
+					return false;
+				}
+				break;
+			}
+		case PGC_INT:
+			{
+				struct config_int *conf = (struct config_int *) gconf;
+
+				if (*conf->variable != 0 && *conf->variable != conf->boot_val)
+				{
+					elog(LOG, "GUC (PGC_INT) %s, boot_val=%d, C-var=%d",
+						 conf->gen.name, conf->boot_val, *conf->variable);
+					return false;
+				}
+				break;
+			}
+		case PGC_REAL:
+			{
+				struct config_real *conf = (struct config_real *) gconf;
+
+				if (*conf->variable != 0.0 && *conf->variable != conf->boot_val)
+				{
+					elog(LOG, "GUC (PGC_REAL) %s, boot_val=%g, C-var=%g",
+						 conf->gen.name, conf->boot_val, *conf->variable);
+					return false;
+				}
+				break;
+			}
+		case PGC_STRING:
+			{
+				struct config_string *conf = (struct config_string *) gconf;
+
+				if (*conf->variable != NULL && strcmp(*conf->variable, conf->boot_val) != 0)
+				{
+					elog(LOG, "GUC (PGC_STRING) %s, boot_val=%s, C-var=%s",
+						 conf->gen.name, conf->boot_val ? conf->boot_val : "<null>", *conf->variable);
+					return false;
+				}
+				break;
+			}
+		case PGC_ENUM:
+			{
+				struct config_enum *conf = (struct config_enum *) gconf;
+
+				if (*conf->variable != conf->boot_val)
+				{
+					elog(LOG, "GUC (PGC_ENUM) %s, boot_val=%d, C-var=%d",
+						 conf->gen.name, conf->boot_val, *conf->variable);
+					return false;
+				}
+				break;
+			}
+	}
+
+	return true;
+}
+#endif
 
 /*
  * Initialize GUC options during program startup.
@@ -1413,6 +1496,9 @@ InitializeGUCOptions(void)
 	hash_seq_init(&status, guc_hashtab);
 	while ((hentry = (GUCHashEntry *) hash_seq_search(&status)) != NULL)
 	{
+		/* check mapping between initial and default value */
+		Assert(check_GUC_init(hentry->gucvar));
+
 		InitializeOneGUCOption(hentry->gucvar);
 	}
 
@@ -4654,6 +4740,9 @@ define_custom_variable(struct config_generic *variable)
 	GUCHashEntry *hentry;
 	struct config_string *pHolder;
 
+	/* check mapping between initial and default value */
+	Assert(check_GUC_init(variable));
+
 	/*
 	 * See if there's a placeholder by the same name.
 	 */
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 05ab087934..836b49484a 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -526,7 +526,7 @@ int			ssl_renegotiation_limit;
  * This really belongs in pg_shmem.c, but is defined here so that it doesn't
  * need to be duplicated in all the different implementations of pg_shmem.c.
  */
-int			huge_pages;
+int			huge_pages = HUGE_PAGES_TRY;
 int			huge_page_size;
 
 /*
@@ -543,7 +543,14 @@ static char *locale_ctype;
 static char *server_encoding_string;
 static char *server_version_string;
 static int	server_version_num;
-static int	syslog_facility;
+
+#ifdef HAVE_SYSLOG
+#define	DEFAULT_SYSLOG_FACILITY LOG_LOCAL0
+#else
+#define	DEFAULT_SYSLOG_FACILITY 0
+#endif
+static int	syslog_facility = DEFAULT_SYSLOG_FACILITY;
+
 static char *timezone_string;
 static char *log_timezone_string;
 static char *timezone_abbreviations_string;
@@ -559,7 +566,14 @@ static int	shared_memory_size_in_huge_pages;
 static int	wal_block_size;
 static bool data_checksums;
 static bool integer_datetimes;
-static bool assert_enabled;
+
+#ifdef USE_ASSERT_CHECKING
+#define DEFAULT_ASSERT_ENABLED true
+#else
+#define DEFAULT_ASSERT_ENABLED false
+#endif
+static bool assert_enabled = DEFAULT_ASSERT_ENABLED;
+
 static char *recovery_target_timeline_string;
 static char *recovery_target_string;
 static char *recovery_target_xid_string;
@@ -1181,11 +1195,7 @@ struct config_bool ConfigureNamesBool[] =
 			GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
 		},
 		&assert_enabled,
-#ifdef USE_ASSERT_CHECKING
-		true,
-#else
-		false,
-#endif
+		DEFAULT_ASSERT_ENABLED,
 		NULL, NULL, NULL
 	},
 
@@ -1357,11 +1367,7 @@ struct config_bool ConfigureNamesBool[] =
 			gettext_noop("Enables updating of the process title every time a new SQL command is received by the server.")
 		},
 		&update_process_title,
-#ifdef WIN32
-		false,
-#else
-		true,
-#endif
+		DEFAULT_UPDATE_PROCESS_TITLE,
 		NULL, NULL, NULL
 	},
 
@@ -2888,11 +2894,7 @@ struct config_int ConfigureNamesInt[] =
 			GUC_EXPLAIN
 		},
 		&effective_io_concurrency,
-#ifdef USE_PREFETCH
-		1,
-#else
-		0,
-#endif
+		DEFAULT_EFFECTIVE_IO_CONCURRENCY,
 		0, MAX_IO_CONCURRENCY,
 		check_effective_io_concurrency, NULL, NULL
 	},
@@ -2906,11 +2908,7 @@ struct config_int ConfigureNamesInt[] =
 			GUC_EXPLAIN
 		},
 		&maintenance_io_concurrency,
-#ifdef USE_PREFETCH
-		10,
-#else
-		0,
-#endif
+		DEFAULT_MAINTENANCE_IO_CONCURRENCY,
 		0, MAX_IO_CONCURRENCY,
 		check_maintenance_io_concurrency, assign_maintenance_io_concurrency,
 		NULL
@@ -4613,11 +4611,7 @@ struct config_enum ConfigureNamesEnum[] =
 			NULL
 		},
 		&syslog_facility,
-#ifdef HAVE_SYSLOG
-		LOG_LOCAL0,
-#else
-		0,
-#endif
+		DEFAULT_SYSLOG_FACILITY,
 		syslog_facility_options,
 		NULL, assign_syslog_facility, NULL
 	},
diff --git a/src/backend/utils/misc/ps_status.c b/src/backend/utils/misc/ps_status.c
index 8520ce76bb..d81a67be79 100644
--- a/src/backend/utils/misc/ps_status.c
+++ b/src/backend/utils/misc/ps_status.c
@@ -30,8 +30,9 @@
 #include "utils/ps_status.h"
 
 extern char **environ;
-bool		update_process_title = true;
 
+/* GUC variable */
+bool		update_process_title = DEFAULT_UPDATE_PROCESS_TITLE;
 
 /*
  * Alternative ways of updating ps display:
diff --git a/contrib/auth_delay/auth_delay.c b/contrib/auth_delay/auth_delay.c
index c3d78e5020..4ca9b4afb1 100644
--- a/contrib/auth_delay/auth_delay.c
+++ b/contrib/auth_delay/auth_delay.c
@@ -21,7 +21,7 @@
 PG_MODULE_MAGIC;
 
 /* GUC Variables */
-static int	auth_delay_milliseconds;
+static int	auth_delay_milliseconds = 0;
 
 /* Original Hook */
 static ClientAuthentication_hook_type original_client_auth_hook = NULL;
diff --git a/contrib/pg_prewarm/autoprewarm.c b/contrib/pg_prewarm/autoprewarm.c
index 1843b1862e..fe002b17e0 100644
--- a/contrib/pg_prewarm/autoprewarm.c
+++ b/contrib/pg_prewarm/autoprewarm.c
@@ -103,7 +103,7 @@ static AutoPrewarmSharedState *apw_state = NULL;
 
 /* GUC variables. */
 static bool autoprewarm = true; /* start worker? */
-static int	autoprewarm_interval;	/* dump interval */
+static int	autoprewarm_interval = 300;	/* dump interval */
 
 /*
  * Module load callback.
diff --git a/contrib/pg_stat_statements/pg_stat_statements.c b/contrib/pg_stat_statements/pg_stat_statements.c
index e5aa429995..198e4e84ad 100644
--- a/contrib/pg_stat_statements/pg_stat_statements.c
+++ b/contrib/pg_stat_statements/pg_stat_statements.c
@@ -283,11 +283,11 @@ static const struct config_enum_entry track_options[] =
 	{NULL, 0, false}
 };
 
-static int	pgss_max;			/* max # statements to track */
-static int	pgss_track;			/* tracking level */
-static bool pgss_track_utility; /* whether to track utility commands */
-static bool pgss_track_planning;	/* whether to track planning duration */
-static bool pgss_save;			/* whether to save stats across shutdown */
+static int	pgss_max = 5000;			/* max # statements to track */
+static int	pgss_track = PGSS_TRACK_TOP;			/* tracking level */
+static bool pgss_track_utility = true; /* whether to track utility commands */
+static bool pgss_track_planning = false ;	/* whether to track planning duration */
+static bool pgss_save = true;			/* whether to save stats across shutdown */
 
 
 #define pgss_enabled(level) \
diff --git a/contrib/pg_trgm/trgm_op.c b/contrib/pg_trgm/trgm_op.c
index 154346398a..2c644bc148 100644
--- a/contrib/pg_trgm/trgm_op.c
+++ b/contrib/pg_trgm/trgm_op.c
@@ -68,7 +68,7 @@ _PG_init(void)
 							 "Sets the threshold used by the % operator.",
 							 "Valid range is 0.0 .. 1.0.",
 							 &similarity_threshold,
-							 0.3,
+							 0.3f,
 							 0.0,
 							 1.0,
 							 PGC_USERSET,
@@ -80,7 +80,7 @@ _PG_init(void)
 							 "Sets the threshold used by the <% operator.",
 							 "Valid range is 0.0 .. 1.0.",
 							 &word_similarity_threshold,
-							 0.6,
+							 0.6f,
 							 0.0,
 							 1.0,
 							 PGC_USERSET,
@@ -92,7 +92,7 @@ _PG_init(void)
 							 "Sets the threshold used by the <<% operator.",
 							 "Valid range is 0.0 .. 1.0.",
 							 &strict_word_similarity_threshold,
-							 0.5,
+							 0.5f,
 							 0.0,
 							 1.0,
 							 PGC_USERSET,
diff --git a/contrib/sepgsql/hooks.c b/contrib/sepgsql/hooks.c
index 87fdd972c2..363ac06700 100644
--- a/contrib/sepgsql/hooks.c
+++ b/contrib/sepgsql/hooks.c
@@ -57,7 +57,7 @@ static sepgsql_context_info_t sepgsql_context_info;
 /*
  * GUC: sepgsql.permissive = (on|off)
  */
-static bool sepgsql_permissive;
+static bool sepgsql_permissive = false;
 
 bool
 sepgsql_get_permissive(void)
@@ -68,7 +68,7 @@ sepgsql_get_permissive(void)
 /*
  * GUC: sepgsql.debug_audit = (on|off)
  */
-static bool sepgsql_debug_audit;
+static bool sepgsql_debug_audit = false;
 
 bool
 sepgsql_get_debug_audit(void)
-- 
2.37.2