Make vacuum_defer_cleanup_age be PGC_SIGHUP level, since it's not sensible

to have different values in different processes of the primary server.
Also put it into the "Streaming Replication" GUC category; it doesn't belong
in "Standby Servers" because you use it on the master not the standby.
In passing also correct guc.c's idea of wal_keep_segments' category.

3 files changed, 15 insertions, 7 deletions

diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index 8cef305239f..9163bc68c41 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -37,7 +37,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/ipc/procarray.c,v 1.70 2010/05/14 07:11:49 sriggs Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/ipc/procarray.c,v 1.71 2010/07/03 21:23:58 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1117,7 +1117,15 @@ GetOldestXmin(bool allDbs, bool ignoreVacuum)
 	LWLockRelease(ProcArrayLock);
 
 	/*
-	 * Compute the cutoff XID, being careful not to generate a "permanent" XID
+	 * Compute the cutoff XID, being careful not to generate a "permanent" XID.
+	 *
+	 * vacuum_defer_cleanup_age provides some additional "slop" for the
+	 * benefit of hot standby queries on slave servers.  This is quick and
+	 * dirty, and perhaps not all that useful unless the master has a
+	 * predictable transaction rate, but it's what we've got.  Note that
+	 * we are assuming vacuum_defer_cleanup_age isn't large enough to cause
+	 * wraparound --- so guc.c should limit it to no more than the xidStopLimit
+	 * threshold in varsup.c.
 	 */
 	result -= vacuum_defer_cleanup_age;
 	if (!TransactionIdIsNormal(result))
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index f2caad2cd9a..ac7f1a26fc2 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -10,7 +10,7 @@
  * Written by Peter Eisentraut <peter_e@gmx.net>.
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/misc/guc.c,v 1.558 2010/07/03 20:43:58 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/misc/guc.c,v 1.559 2010/07/03 21:23:58 tgl Exp $
  *
  *--------------------------------------------------------------------
  */
@@ -1631,8 +1631,8 @@ static struct config_int ConfigureNamesInt[] =
 	},
 
 	{
-		{"vacuum_defer_cleanup_age", PGC_USERSET, WAL_STANDBY_SERVERS,
-			gettext_noop("Age by which VACUUM and HOT cleanup should be deferred, if any."),
+		{"vacuum_defer_cleanup_age", PGC_SIGHUP, WAL_REPLICATION,
+			gettext_noop("Number of transactions by which VACUUM and HOT cleanup should be deferred, if any."),
 			NULL
 		},
 		&vacuum_defer_cleanup_age,
@@ -1675,7 +1675,7 @@ static struct config_int ConfigureNamesInt[] =
 	},
 
 	{
-		{"wal_keep_segments", PGC_SIGHUP, WAL_CHECKPOINTS,
+		{"wal_keep_segments", PGC_SIGHUP, WAL_REPLICATION,
 			gettext_noop("Sets the number of WAL files held for standby servers."),
 			NULL
 		},
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index e765664ecc0..a3b145796d0 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -188,6 +188,7 @@
 #max_wal_senders = 0		# max number of walsender processes
 #wal_sender_delay = 200ms	# 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
 
 # - Standby Servers -
 
@@ -198,7 +199,6 @@
 #max_standby_streaming_delay = 30s	# max delay before canceling queries
 					# when reading streaming WAL;
 					# -1 allows indefinite delay
-#vacuum_defer_cleanup_age = 0		# number of transactions by which cleanup is deferred
 
 
 #------------------------------------------------------------------------------