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.

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 391e4365c0c59aafa73db924cbdba72075b392bb..86bf6ee91212e5ea25dabd9dafd681cdb31ca698 100644 (file)
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -1,4 +1,4 @@
-<!-- $PostgreSQL: pgsql/doc/src/sgml/config.sgml,v 1.289 2010/07/03 20:43:57 tgl Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/config.sgml,v 1.290 2010/07/03 21:23:58 tgl Exp $ -->
 
 <chapter Id="runtime-config">
   <title>Server Configuration</title>
@@ -1914,6 +1914,31 @@ SET ENABLE_SEQSCAN TO OFF;
        </para>
        </listitem>
       </varlistentry>
+
+     <varlistentry id="guc-vacuum-defer-cleanup-age" xreflabel="vacuum_defer_cleanup_age">
+      <term><varname>vacuum_defer_cleanup_age</varname> (<type>integer</type>)</term>
+      <indexterm>
+       <primary><varname>vacuum_defer_cleanup_age</> configuration parameter</primary>
+      </indexterm>
+      <listitem>
+       <para>
+        Specifies the number of transactions by which <command>VACUUM</> and
+        <acronym>HOT</> updates will defer cleanup of dead row versions. The
+        default is zero transactions, meaning that dead row versions can be
+        removed as soon as possible, that is, as soon as they are no longer
+        visible to any open transaction.  You may wish to set this to a
+   non-zero value on a primary server that is supporting hot standby
+        servers, as described in <xref linkend="hot-standby">.  This allows
+        more time for queries on the standby to complete without incurring
+        conflicts due to early cleanup of rows.  However, since the value
+        is measured in terms of number of write transactions occurring on the
+        primary server, it is difficult to predict just how much additional
+        grace time will be made available to standby queries.
+        This parameter can only be set in the <filename>postgresql.conf</>
+        file or on the server command line.
+       </para>
+      </listitem>
+     </varlistentry>
      </variablelist>
     </sect2>
 
@@ -2004,29 +2029,6 @@ SET ENABLE_SEQSCAN TO OFF;
       </listitem>
      </varlistentry>
 
-     <varlistentry id="guc-vacuum-defer-cleanup-age" xreflabel="vacuum_defer_cleanup_age">
-      <term><varname>vacuum_defer_cleanup_age</varname> (<type>integer</type>)</term>
-      <indexterm>
-       <primary><varname>vacuum_defer_cleanup_age</> configuration parameter</primary>
-      </indexterm>
-      <listitem>
-       <para>
-        Specifies the number of transactions by which <command>VACUUM</> and
-        <acronym>HOT</> updates will defer cleanup of dead row versions. The
-        default is 0 transactions, meaning that dead row versions will be
-        removed as soon as possible. You may wish to set this to a non-zero
-        value when planning or maintaining a Hot Standby connection, as
-        described in <xref linkend="hot-standby">.  The recommended value is
-        <literal>0</> unless you have clear reason to increase it. The purpose
-        of the parameter is to allow the user to specify an approximate time
-        delay before cleanup occurs. However, it should be noted that there is
-        no direct link with any specific time delay and so the results will be
-        application and installation specific, as well as variable over time,
-        depending upon the transaction rate (of writes only).
-       </para>
-      </listitem>
-     </varlistentry>
-
      </variablelist>
     </sect2>
    </sect1>

diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index 8cef305239f05a55b45d821b96335c5b3a2fc3d7..9163bc68c418bacda66dad8f0a2d1b2da21c2dd3 100644 (file)
--- 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 f2caad2cd9a87acd51f4ba53f13e0645cf380e59..ac7f1a26fc2fd32f6226f3713a6cb23adc92cdb2 100644 (file)
--- 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 e765664ecc0d66a2720443a0632143aae01936ad..a3b145796d08f85396f153c8d4fa8d0d821e49a6 100644 (file)
--- 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
 
 
 #------------------------------------------------------------------------------