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Documentation of the system catalogs, directed toward PostgreSQL developers

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about the autovacuum daemon, see <xref linkend="autovacuum">.

</para>

<note>

<para>

It is likely that <structname>pg_autovacuum</structname> will disappear

in a future release, with the information instead being kept in

<structname>pg_class</>.<structfield>reloptions</> entries.

</para>

</note>

<table>

<title><structname>pg_autovacuum</> Columns</title>

<entry><structfield>enabled</structfield></entry>

<entry><type>bool</type></entry>

<entry></entry>

<entry>If false, this table is never autovacuumed</entry>

<entry>If false, this table will not be autovacuumed, except

to prevent transaction ID wraparound</entry>

</row>

<row>

to prevent transaction ID wraparound if the table's

<structname>pg_class</>.<structfield>relfrozenxid</> field attains an age

of more than <structfield>freeze_max_age</> transactions, whether the table

has been changed or not. The system will launch autovacuum to perform

has been changed or not, even if

<structname>pg_autovacuum</>.<structfield>enabled</> is set to

<literal>false</> for it. The system will launch autovacuum to perform

such <command>VACUUM</>s even if autovacuum is otherwise disabled.

See <xref linkend="vacuum-for-wraparound"> for more about wraparound

prevention.

be used for this particular value. Observe that the

<structfield>vac_cost_delay</> variable inherits its default value from the

<xref linkend="guc-autovacuum-vacuum-cost-delay"> configuration parameter,

or from <xref linkend="guc-vacuum-cost-delay"> if the former is set to a negative

value. The same applies to <structfield>vac_cost_limit</>.

or from <xref linkend="guc-vacuum-cost-delay"> if the former is set to a

negativevalue. The same applies to <structfield>vac_cost_limit</>.

Also, autovacuum will ignore attempts to set a per-table

<structfield>freeze_max_age</> larger than the system-wide setting (it can only be set

smaller), and the <structfield>freeze_min_age value</> will be limited to half the

system-wide <xref linkend="guc-autovacuum-freeze-max-age"> setting.

<structfield>freeze_max_age</> larger than the system-wide setting (it can

only be set smaller), and the <structfield>freeze_min_age</> value will be

limited to half the system-wide <xref

linkend="guc-autovacuum-freeze-max-age"> setting. Note that while you

can set <structfield>freeze_max_age</> very small, or even zero, this

is usually unwise since it will force frequent vacuuming.

</para>

</sect1>