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Update autovacuum to use reloptions instead of a system catalog, for

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per-table overrides of parameters.

This removes a whole class of problems related to misusing the catalog,
and perhaps more importantly, gives us pg_dump support for the parameters.

Based on a patch by Euler Taveira de Oliveira, heavily reworked by me.
This commit is contained in:
Alvaro Herrera
2009-02-09 20:57:59 +00:00
parent 57b10ebcd4
commit 834a6da4f7
13 changed files with 421 additions and 483 deletions
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76
doc/src/sgml/maintenance.sgml
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@@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/maintenance.sgml,v 1.89 2009/01/16 13:27:23 heikki Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/maintenance.sgml,v 1.90 2009/02/09 20:57:59 alvherre Exp $ -->
<chapter id="maintenance">
<title>Routine Database Maintenance Tasks</title>
@@ -573,7 +573,9 @@ HINT: Stop the postmaster and use a standalone backend to VACUUM in "mydb".
<para>
Tables whose <structfield>relfrozenxid</> value is more than
<varname>autovacuum_freeze_max_age</> transactions old are always
vacuumed. Otherwise, if the number of tuples obsoleted since the last
vacuumed (this also applies to those tables whose freeze max age has
been modified via storage parameters; see below). Otherwise, if the
number of tuples obsoleted since the last
<command>VACUUM</command> exceeds the <quote>vacuum threshold</quote>, the
table is vacuumed. The vacuum threshold is defined as:
<programlisting>
@@ -604,65 +606,39 @@ analyze threshold = analyze base threshold + analyze scale factor * number of tu
<para>
The default thresholds and scale factors are taken from
<filename>postgresql.conf</filename>, but it is possible to override them
on a table-by-table basis by making entries in the system catalog
<link
linkend="catalog-pg-autovacuum"><structname>pg_autovacuum</></link>.
If a <structname>pg_autovacuum</structname> row exists for a particular
table, the settings it specifies are applied; otherwise the global
settings are used. See <xref linkend="runtime-config-autovacuum"> for
on a table-by-table basis; see
<xref linkend="sql-createtable-storage-parameters"
endterm="sql-createtable-storage-parameters-title"> for more information.
If a setting
has been changed via storage parameters, that value is used; otherwise the
global settings are used. See <xref linkend="runtime-config-autovacuum"> for
more details on the global settings.
</para>
<para>
Besides the base threshold values and scale factors, there are five
more parameters that can be set for each table in
<structname>pg_autovacuum</structname>.
The first, <structname>pg_autovacuum</>.<structfield>enabled</>,
Besides the base threshold values and scale factors, there are six
more autovacuum parameters that can be set for each table via
storage parameters.
The first parameter, <literal>autovacuum_enabled</>,
can be set to <literal>false</literal> to instruct the autovacuum daemon
to skip that particular table entirely. In this case
autovacuum will only touch the table if it must do so
to prevent transaction ID wraparound.
The next two parameters, the vacuum cost delay
(<structname>pg_autovacuum</structname>.<structfield>vac_cost_delay</structfield>)
and the vacuum cost limit
(<structname>pg_autovacuum</structname>.<structfield>vac_cost_limit</structfield>),
are used to set table-specific values for the
<xref linkend="runtime-config-resource-vacuum-cost" endterm="runtime-config-resource-vacuum-cost-title">
Another two parameters,
<literal>autovacuum_vacuum_cost_delay</literal> and
<literal>autovacuum_vacuum_cost_limit</literal>, are used to set
table-specific values for the
<xref linkend="runtime-config-resource-vacuum-cost"
endterm="runtime-config-resource-vacuum-cost-title">
feature.
The last two parameters,
(<structname>pg_autovacuum</structname>.<structfield>freeze_min_age</structfield>)
and
(<structname>pg_autovacuum</structname>.<structfield>freeze_max_age</structfield>),
are used to set table-specific values for
<xref linkend="guc-vacuum-freeze-min-age"> and
<xref linkend="guc-autovacuum-freeze-max-age"> respectively.
<literal>autovacuum_freeze_min_age</literal>,
<literal>autovacuum_freeze_max_age</literal> and
<literal>autovacuum_freeze_table_age</literal> are used to set
values for <xref linkend="guc-vacuum-freeze-min-age">,
<xref linkend="guc-autovacuum-freeze-max-age"> and
<xref linkend="guc-vacuum-freeze-table-age"> respectively.
</para>
<para>
If any of the values in <structname>pg_autovacuum</structname>
are set to a negative number, or if a row is not present at all in
<structname>pg_autovacuum</structname> for any particular table, the
corresponding values from <filename>postgresql.conf</filename> are used.
</para>
<para>
There is not currently any support for making
<structname>pg_autovacuum</structname> entries, except by doing
manual <command>INSERT</>s into the catalog. This feature will be
improved in future releases, and it is likely that the catalog
definition will change.
</para>
<caution>
<para>
The contents of the <structname>pg_autovacuum</structname> system
catalog are currently not saved in database dumps created by the
tools <application>pg_dump</> and <application>pg_dumpall</>. If
you want to preserve them across a dump/reload cycle, make sure
you dump the catalog manually.
</para>
</caution>
<para>
When multiple workers are running, the cost limit is
<quote>balanced</quote> among all the running workers, so that the