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Limit concurrent backend WAL flushers #2

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Limit concurrent backend WAL flushers #2

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b2222fe
Limit concurrent backend WAL flushers
vbp1 Jul 3, 2026
2ff7a08
Rework limited backend WAL flushing onto a ConditionVariable
vbp1 Jul 4, 2026
86b5dbe
Pad limited-flush shared state away from info_lck
vbp1 Jul 4, 2026
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23 changes: 23 additions & 0 deletions doc/src/sgml/config.sgml
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Original file line number Diff line number Diff line change
Expand Up @@ -3591,6 +3591,29 @@ include_dir 'conf.d'
</listitem>
</varlistentry>

<varlistentry id="guc-wal-flush-backend-flushers" xreflabel="wal_flush_backend_flushers">
<term><varname>wal_flush_backend_flushers</varname> (<type>integer</type>)
<indexterm>
<primary><varname>wal_flush_backend_flushers</varname> configuration parameter</primary>
</indexterm>
</term>
<listitem>
<para>
Sets the maximum number of client backends that can flush WAL
concurrently. When the limit is reached, further backends needing
their WAL flushed wait until one of the active flushers has flushed
it for them, or until they are allowed to flush themselves. This
can reduce contention on WAL flushing with very many concurrently
committing sessions. Background processes, such as autovacuum
workers and background workers, are not subject to this limit.
The value <literal>0</literal>, which is the default, disables the
limit. This parameter can only be set in the
<filename>postgresql.conf</filename> file or on the server command
line.
</para>
</listitem>
</varlistentry>

<varlistentry id="guc-wal-skip-threshold" xreflabel="wal_skip_threshold">
<term><varname>wal_skip_threshold</varname> (<type>integer</type>)
<indexterm>
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