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Commite2a186b

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Add a multi-worker capability to autovacuum. This allows multiple worker
processes to be running simultaneously. Also, now autovacuum processes do notcount towards the max_connections limit; they are counted separately fromregular processes, and are limited by the new GUC variableautovacuum_max_workers.The launcher now has intelligence to launch workers on each database everyautovacuum_naptime seconds, limited only on the max amount of worker slotsavailable.Also, the global worker I/O utilization is limited by the vacuum cost-baseddelay feature. Workers are "balanced" so that the total I/O consumption doesnot exceed the established limit. This part of the patch was contributed byITAGAKI Takahiro.Per discussion.
1 parent42dc4b6 commite2a186b

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12 files changed

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-159
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12 files changed

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‎doc/src/sgml/config.sgml‎

Lines changed: 24 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -1,4 +1,4 @@
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<!-- $PostgreSQL: pgsql/doc/src/sgml/config.sgml,v 1.119 2007/04/02 15:27:02 petere Exp $ -->
1+
<!-- $PostgreSQL: pgsql/doc/src/sgml/config.sgml,v 1.120 2007/04/16 18:29:50 alvherre Exp $ -->
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<chapter Id="runtime-config">
44
<title>Server Configuration</title>
@@ -3166,7 +3166,7 @@ SELECT * FROM parent WHERE key = 2400;
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<listitem>
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<para>
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Controls whether the server should run the
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autovacuum daemon. This isoff by default.
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autovacuumlauncherdaemon. This ison by default.
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<varname>stats_start_collector</> and <varname>stats_row_level</>
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must also be turned on for autovacuum to work.
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This parameter can only be set in the <filename>postgresql.conf</>
@@ -3175,16 +3175,31 @@ SELECT * FROM parent WHERE key = 2400;
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</listitem>
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</varlistentry>
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<varlistentry id="guc-autovacuum-max-workers" xreflabel="autovacuum_max_workers">
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<term><varname>autovacuum_max_workers</varname> (<type>integer</type>)</term>
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<indexterm>
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<primary><varname>autovacuum_max_workers</> configuration parameter</primary>
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</indexterm>
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<listitem>
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<para>
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Specifies the maximum number of autovacuum processes (other than the
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autovacuum launcher) which may be running at any one time. The default
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is three (<literal>3</literal>). This parameter can only be set in
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the <filename>postgresql.conf</> file or on the server command line.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry id="guc-autovacuum-naptime" xreflabel="autovacuum_naptime">
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<term><varname>autovacuum_naptime</varname> (<type>integer</type>)</term>
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<indexterm>
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<primary><varname>autovacuum_naptime</> configuration parameter</primary>
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</indexterm>
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<listitem>
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<para>
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Specifies the delay betweenactivity rounds for the autovacuum
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daemon. In each round the daemon examinesone database
3187-
and issues <command>VACUUM</> and <command>ANALYZE</> commands
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Specifies theminimumdelay betweenautovacuum runs on any given
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database. In each round the daemon examinesthe
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databaseand issues <command>VACUUM</> and <command>ANALYZE</> commands
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as needed for tables in that database. The delay is measured
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in seconds, and the default is one minute (<literal>1m</>).
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This parameter can only be set in the <filename>postgresql.conf</>
@@ -3318,7 +3333,10 @@ SELECT * FROM parent WHERE key = 2400;
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Specifies the cost limit value that will be used in automatic
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<command>VACUUM</> operations. If <literal>-1</> is specified (which is the
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default), the regular
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<xref linkend="guc-vacuum-cost-limit"> value will be used.
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<xref linkend="guc-vacuum-cost-limit"> value will be used. Note that
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the value is distributed proportionally among the running autovacuum
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workers, if there is more than one, so that the sum of the limits of
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each worker never exceeds the limit on this variable.
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This parameter can only be set in the <filename>postgresql.conf</>
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file or on the server command line.
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This setting can be overridden for individual tables by entries in

‎doc/src/sgml/maintenance.sgml‎

Lines changed: 36 additions & 13 deletions
Original file line numberDiff line numberDiff line change
@@ -1,4 +1,4 @@
1-
<!-- $PostgreSQL: pgsql/doc/src/sgml/maintenance.sgml,v 1.70 2007/02/01 19:10:24 momjian Exp $ -->
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<!-- $PostgreSQL: pgsql/doc/src/sgml/maintenance.sgml,v 1.71 2007/04/16 18:29:50 alvherre Exp $ -->
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<chapter id="maintenance">
44
<title>Routine Database Maintenance Tasks</title>
@@ -466,26 +466,43 @@ HINT: Stop the postmaster and use a standalone backend to VACUUM in "mydb".
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<secondary>general information</secondary>
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</indexterm>
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<para>
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Beginning in <productname>PostgreSQL</productname> 8.1, there isa
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separateoptionalserver processcalledthe<firstterm>autovacuum
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daemon</firstterm>,whose purpose is to automate the execution of
469+
Beginning in <productname>PostgreSQL</productname> 8.1, there isan
470+
optionalfeaturecalled <firstterm>autovacuum</firstterm>,
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whose purpose is to automate the execution of
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<command>VACUUM</command> and <command>ANALYZE </command> commands.
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When enabled,theautovacuum daemon runs periodically and checks for
473+
When enabled, autovacuum checks for
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tables that have had a large number of inserted, updated or deleted
475475
tuples. These checks use the row-level statistics collection facility;
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therefore,theautovacuum daemon cannot be used unless <xref
476+
therefore, autovacuum cannot be used unless <xref
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linkend="guc-stats-start-collector"> and <xref
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linkend="guc-stats-row-level"> are set to <literal>true</literal>. Also,
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it's important to allow a slot for the autovacuum process when choosing
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the value of <xref linkend="guc-superuser-reserved-connections">. In
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the default configuration, autovacuuming is enabled and the related
478+
linkend="guc-stats-row-level"> are set to <literal>true</literal>.
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In the default configuration, autovacuuming is enabled and the related
482480
configuration parameters are appropriately set.
483481
</para>
484482

485483
<para>
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The autovacuum daemon, when enabled, runs every <xref
487-
linkend="guc-autovacuum-naptime"> seconds. On each run, it selects
488-
one database to process and checks each table within that database.
484+
Beginning in <productname>PostgreSQL</productname> 8.3, autovacuum has a
485+
multi-process architecture: there is a daemon process, called the
486+
<firstterm>autovacuum launcher</firstterm>, which is in charge of starting
487+
an <firstterm>autovacuum worker</firstterm> process on each database every
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<xref linkend="guc-autovacuum-naptime"> seconds.
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</para>
490+
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<para>
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There is a limit of <xref linkend="guc-autovacuum-max-workers"> worker
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processes that may be running at at any time, so if the <command>VACUUM</>
494+
and <command>ANALYZE</> work to do takes too long to run, the deadline may
495+
be failed to meet for other databases. Also, if a particular database
496+
takes long to process, more than one worker may be processing it
497+
simultaneously. The workers are smart enough to avoid repeating work that
498+
other workers have done, so this is normally not a problem. Note that the
499+
number of running workers does not count towards the <xref
500+
linkend="guc-max-connections"> nor the <xref
501+
linkend="guc-superuser-reserved-connections"> limits.
502+
</para>
503+
504+
<para>
505+
On each run, the worker process checks each table within that database, and
489506
<command>VACUUM</command> or <command>ANALYZE</command> commands are
490507
issued as needed.
491508
</para>
@@ -581,6 +598,12 @@ analyze threshold = analyze base threshold + analyze scale factor * number of tu
581598
</para>
582599
</caution>
583600

601+
<para>
602+
When multiple workers are running, the cost limit is "balanced" among all
603+
the running workers, so that the total impact on the system is the same,
604+
regardless of the number of workers actually running.
605+
</para>
606+
584607
</sect2>
585608
</sect1>
586609

‎src/backend/commands/vacuum.c‎

Lines changed: 4 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -13,7 +13,7 @@
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*
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.349 2007/03/14 18:48:55 tgl Exp $
16+
* $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.350 2007/04/16 18:29:50 alvherre Exp $
1717
*
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*-------------------------------------------------------------------------
1919
*/
@@ -3504,6 +3504,9 @@ vacuum_delay_point(void)
35043504

35053505
VacuumCostBalance=0;
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3507+
/* update balance values for workers */
3508+
AutoVacuumUpdateDelay();
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35073510
/* Might have gotten an interrupt while sleeping */
35083511
CHECK_FOR_INTERRUPTS();
35093512
}

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