Merge synchronous_replication setting into synchronous_commit.

This means one less thing to configure when setting up synchronous
replication, and also avoids some ambiguity around what the behavior
should be when the settings of these variables conflict.

Fujii Masao, with additional hacking by me.

src/backend/access/transam/xact.c

@@ -68,7 +68,7 @@ bool		XactReadOnly;
 bool		DefaultXactDeferrable = false;
 bool		XactDeferrable;
 
-bool		XactSyncCommit = true;
+int			synchronous_commit = SYNCHRONOUS_COMMIT_ON;
 
 int			CommitDelay = 0;	/* precommit delay in microseconds */
 int			CommitSiblings = 5; /* # concurrent xacts needed to sleep */
@@ -1056,7 +1056,8 @@ RecordTransactionCommit(void)
 	 * if all to-be-deleted tables are temporary though, since they are lost
 	 * anyway if we crash.)
 	 */
-	if ((wrote_xlog && XactSyncCommit) || forceSyncCommit || nrels > 0 || SyncRepRequested())
+	if ((wrote_xlog && synchronous_commit >= SYNCHRONOUS_COMMIT_LOCAL) ||
+		forceSyncCommit || nrels > 0)
 	{
 		/*
 		 * Synchronous commit case:

src/backend/postmaster/autovacuum.c

@@ -1531,7 +1531,8 @@ AutoVacWorkerMain(int argc, char *argv[])
 	 * if we are waiting for standbys to connect. This is important to
 	 * ensure we aren't blocked from performing anti-wraparound tasks.
 	 */
-	SetConfigOption("synchronous_replication", "off", PGC_SUSET, PGC_S_OVERRIDE);
+	if (synchronous_commit == SYNCHRONOUS_COMMIT_ON)
+		SetConfigOption("synchronous_commit", "local", PGC_SUSET, PGC_S_OVERRIDE);
 
 	/*
 	 * Get the info about the database we're going to work on.

src/backend/replication/syncrep.c

@@ -63,7 +63,6 @@
 #include "utils/ps_status.h"
 
 /* User-settable parameters for sync rep */
-bool	synchronous_replication = false;		/* Only set in user backends */
 char 	*SyncRepStandbyNames;
 
 #define SyncStandbysDefined() \

src/backend/utils/misc/guc.c

@@ -350,6 +350,23 @@ static const struct config_enum_entry constraint_exclusion_options[] = {
 	{NULL, 0, false}
 };
 
+/*
+ * Although only "on", "off", and "local" are documented, we
+ * accept all the likely variants of "on" and "off".
+ */
+static const struct config_enum_entry synchronous_commit_options[] = {
+	{"local", SYNCHRONOUS_COMMIT_LOCAL, false},
+	{"on", SYNCHRONOUS_COMMIT_ON, false},
+	{"off", SYNCHRONOUS_COMMIT_OFF, false},
+	{"true", SYNCHRONOUS_COMMIT_ON, true},
+	{"false", SYNCHRONOUS_COMMIT_OFF, true},
+	{"yes", SYNCHRONOUS_COMMIT_ON, true},
+	{"no", SYNCHRONOUS_COMMIT_OFF, true},
+	{"1", SYNCHRONOUS_COMMIT_ON, true},
+	{"0", SYNCHRONOUS_COMMIT_OFF, true},
+	{NULL, 0, false}
+};
+
 /*
  * Options for enum values stored in other modules
  */
@@ -746,22 +763,6 @@ static struct config_bool ConfigureNamesBool[] =
 		&enableFsync,
 		true, NULL, NULL
 	},
-	{
-		{"synchronous_commit", PGC_USERSET, WAL_SETTINGS,
-			gettext_noop("Sets immediate fsync at commit."),
-			NULL
-		},
-		&XactSyncCommit,
-		true, NULL, NULL
-	},
-	{
-		{"synchronous_replication", PGC_USERSET, WAL_REPLICATION,
-			gettext_noop("Requests synchronous replication."),
-			NULL
-		},
-		&synchronous_replication,
-		false, NULL, NULL
-	},
 	{
 		{"zero_damaged_pages", PGC_SUSET, DEVELOPER_OPTIONS,
 			gettext_noop("Continues processing past damaged page headers."),
@@ -2908,6 +2909,16 @@ static struct config_enum ConfigureNamesEnum[] =
 		assign_session_replication_role, NULL
 	},
 
+	{
+		{"synchronous_commit", PGC_USERSET, WAL_SETTINGS,
+			gettext_noop("Sets the current transaction's synchronization level."),
+			NULL
+		},
+		&synchronous_commit,
+		SYNCHRONOUS_COMMIT_ON, synchronous_commit_options,
+		NULL, NULL
+	},
+
 	{
 		{"trace_recovery_messages", PGC_SIGHUP, DEVELOPER_OPTIONS,
 			gettext_noop("Enables logging of recovery-related debugging information."),

src/backend/utils/misc/postgresql.conf.sample

@@ -153,7 +153,7 @@
 #wal_level = minimal			# minimal, archive, or hot_standby
 					# (change requires restart)
 #fsync = on				# turns forced synchronization on or off
-#synchronous_commit = on		# immediate fsync at commit
+#synchronous_commit = on		# synchronization level; on, off, or local
 #wal_sync_method = fsync		# the default is the first option
 					# supported by the operating system:
 					#   open_datasync
@@ -184,10 +184,6 @@
 #archive_timeout = 0		# force a logfile segment switch after this
 				# number of seconds; 0 disables
 
-# - Replication - User Settings
-
-#synchronous_replication = off		# does commit wait for reply from standby
-
 # - Streaming Replication - Server Settings
 
 #synchronous_standby_names = ''	# standby servers that provide sync rep

src/include/access/xact.h

@@ -52,8 +52,15 @@ extern bool XactReadOnly;
 extern bool DefaultXactDeferrable;
 extern bool XactDeferrable;
 
-/* Asynchronous commits */
-extern bool XactSyncCommit;
+typedef enum
+{
+	SYNCHRONOUS_COMMIT_OFF,		/* asynchronous commit */
+	SYNCHRONOUS_COMMIT_LOCAL,	/* wait for only local flush */
+	SYNCHRONOUS_COMMIT_ON		/* wait for local flush and sync rep */
+} SyncCommitLevel;
+
+/* Synchronous commit level */
+extern int	synchronous_commit;
 
 /* Kluge for 2PC support */
 extern bool MyXactAccessedTempRel;

src/include/replication/syncrep.h

@@ -20,7 +20,7 @@
 #include "utils/guc.h"
 
 #define SyncRepRequested() \
-	(synchronous_replication && max_wal_senders > 0)
+	(max_wal_senders > 0 && synchronous_commit == SYNCHRONOUS_COMMIT_ON)
 
 /* syncRepState */
 #define SYNC_REP_NOT_WAITING		0
@@ -28,7 +28,6 @@
 #define SYNC_REP_WAIT_COMPLETE		2
 
 /* user-settable parameters for synchronous replication */
-extern bool synchronous_replication;
 extern char *SyncRepStandbyNames;
 
 /* called by user backend */