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Commit62ed5e7

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author
Amit Kapila
committed
Doc: document autovacuum interruption.
It's important users be able to know (without looking at the source code)that running DDL or DDL-like commands can interrupt autovacuum which canlead to a lot of dead tuples and hence slower database operations.Reported-by: James ColemanAuthor: James ColemanReviewed-by: Amit KapilaBackpatch-through: 9.4Discussion:https://postgr.es/m/CAAaqYe-XYyNwML1=f=gnd0qWg46PnvD=BDrCZ5-L94B887XVxQ@mail.gmail.com
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‎doc/src/sgml/maintenance.sgml

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@@ -825,6 +825,26 @@ analyze threshold = analyze base threshold + analyze scale factor * number of tu
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<literal>autovacuum_vacuum_cost_limit</literal> storage parameters have been set
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are not considered in the balancing algorithm.
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</para>
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<para>
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Autovacuum workers generally don't block other commands. If a process
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attempts to acquire a lock that conficts with the
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<literal>SHARE UPDATE EXCLUSIVE</literal> lock held by autovacuum, lock
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acquisition will interrupt the autovacuum. For conflicting lock modes,
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see <xref linkend="table-lock-compatibility"/>. However, if the autovacuum
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is running to prevent transaction ID wraparound (i.e., the autovacuum query
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name in the <structname>pg_stat_activity</structname> view ends with
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<literal>(to prevent wraparound)</literal>), the autovacuum is not
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automatically interrupted.
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</para>
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<warning>
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<para>
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Regularly running commands that acquire locks conflicting with a
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<literal>SHARE UPDATE EXCLUSIVE</literal> lock (e.g., ANALYZE) can
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effectively prevent autovacuums from ever completing.
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</para>
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</warning>
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</sect2>
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</sect1>
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