Increase the default for wal_sender_delay from 200ms to 1s. Now that WAL

sender is immediately woken up by transaction commit, there's no need to
wake up so aggressively.

doc/src/sgml/config.sgml

@@ -1939,8 +1939,11 @@ SET ENABLE_SEQSCAN TO OFF;
         Specifies the delay between activity rounds for WAL sender processes.
         In each round the WAL sender sends any WAL accumulated since the last
         round to the standby server. It then sleeps for
-        <varname>wal_sender_delay</> milliseconds, and repeats. The default
-        value is 200 milliseconds (<literal>200ms</>).
+        <varname>wal_sender_delay</> milliseconds, and repeats. The sleep
+        is interrupted by transaction commit, so the effects of a committed
+        transaction are sent to standby servers as soon as the commit
+        happens, regardless of this setting. The default value is one second
+        (<literal>1s</>).
         Note that on many systems, the effective resolution of sleep delays is
         10 milliseconds; setting <varname>wal_sender_delay</> to a value that
         is not a multiple of 10 might have the same results as setting it to

src/backend/replication/walsender.c

@@ -73,7 +73,7 @@ bool		am_walsender = false;		/* Am I a walsender process ? */
 
 /* User-settable parameters for walsender */
 int			max_wal_senders = 0;	/* the maximum number of concurrent walsenders */
-int			WalSndDelay = 200;	/* max sleep time between some actions */
+int			WalSndDelay = 1000;	/* max sleep time between some actions */
 
 /*
  * These variables are used similarly to openLogFile/Id/Seg/Off,

src/backend/utils/misc/guc.c

@@ -1843,7 +1843,7 @@ static struct config_int ConfigureNamesInt[] =
 			GUC_UNIT_MS
 		},
 		&WalSndDelay,
-		200, 1, 10000, NULL, NULL
+		1000, 1, 10000, NULL, NULL
 	},
 
 	{

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

@@ -188,7 +188,7 @@
 
 #max_wal_senders = 0		# max number of walsender processes
 				# (change requires restart)
-#wal_sender_delay = 200ms	# walsender cycle time, 1-10000 milliseconds
+#wal_sender_delay = 1s		# walsender cycle time, 1-10000 milliseconds
 #wal_keep_segments = 0		# in logfile segments, 16MB each; 0 disables
 #vacuum_defer_cleanup_age = 0	# number of xacts by which cleanup is delayed