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Clearify how processes are started by autovacuum, and what the effect

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of autovacuum_max_workers parameter is.

Per discussion with Alvaro.
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Magnus Hagander 2008-12-08 20:30:58 +00:00
parent 4e0b63b0b9
commit 9edd720050
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doc/src/sgml/maintenance.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/maintenance.sgml,v 1.86 2008/06/16 03:13:14 tgl Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/maintenance.sgml,v 1.87 2008/12/08 20:30:58 mha Exp $ -->
<chapter id="maintenance">
<title>Routine Database Maintenance Tasks</title>
@ -522,10 +522,16 @@ HINT: Stop the postmaster and use a standalone backend to VACUUM in "mydb".
The <quote>autovacuum daemon</> actually consists of multiple processes.
There is a persistent daemon process, called the
<firstterm>autovacuum launcher</firstterm>, which is in charge of starting
an <firstterm>autovacuum worker</firstterm> process on each database every
<xref linkend="guc-autovacuum-naptime"> seconds. On each run, the worker
process checks each table within that database, and executes
<command>VACUUM</> and/or <command>ANALYZE</> commands as needed.
<firstterm>autovacuum worker</firstterm> processes for all databases. The
launcher will distribute the work across time, but attempt to start one
worker on each database every <xref linkend="guc-autovacuum-naptime">
seconds. One worker will be launched for each database, with a maximum
of <xref linkend="guc-autovacuum-max-workers"> processes running at the
same time. If there are more than
<xref linkend="guc-autovacuum-max-workers"> databases to be processed,
the next database will be processed as soon as the first worker finishes.
The worker processes will check each table within its database and
execute <command>VACUUM</> and/or <command>ANALYZE</> as needed.
</para>
<para>