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Rework text in replication slots documentation

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This is cosmetic, so no backpatch.

Reviewed-by: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Discussion: https://postgr.es/m/20230413111838.e7yxke2dtwrxw3qy@alvherre.pgsql
Discussion: https://postgr.es/m/202401151537.ryhysqfncs6d@alvherre.pgsql
This commit is contained in:
Alvaro Herrera
2024-01-18 11:30:53 +01:00
parent ed1e0a6512
commit 27d04ed531
1 changed files with 17 additions and 9 deletions
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26
doc/src/sgml/high-availability.sgml
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@ -924,7 +924,8 @@ primary_conninfo = 'host=192.168.1.50 port=5432 user=foo password=foopass'
<secondary>streaming replication</secondary> <secondary>streaming replication</secondary>
</indexterm> </indexterm>
<para> <para>
Replication slots provide an automated way to ensure that the primary does Replication slots provide an automated way to ensure that the
primary server does
not remove WAL segments until they have been received by all standbys, not remove WAL segments until they have been received by all standbys,
and that the primary does not remove rows which could cause a and that the primary does not remove rows which could cause a
<link linkend="hot-standby-conflict">recovery conflict</link> even when the <link linkend="hot-standby-conflict">recovery conflict</link> even when the
@ -935,21 +936,28 @@ primary_conninfo = 'host=192.168.1.50 port=5432 user=foo password=foopass'
of old WAL segments using <xref linkend="guc-wal-keep-size"/>, or by of old WAL segments using <xref linkend="guc-wal-keep-size"/>, or by
storing the segments in an archive using storing the segments in an archive using
<xref linkend="guc-archive-command"/> or <xref linkend="guc-archive-library"/>. <xref linkend="guc-archive-command"/> or <xref linkend="guc-archive-library"/>.
However, these methods often result in retaining more WAL segments than A disadvantage of these methods is that they
often result in retaining more WAL segments than
required, whereas replication slots retain only the number of segments required, whereas replication slots retain only the number of segments
known to be needed. On the other hand, replication slots can retain so known to be needed.
many WAL segments that they fill up the space allocated
for <literal>pg_wal</literal>;
<xref linkend="guc-max-slot-wal-keep-size"/> limits the size of WAL files
retained by replication slots.
</para> </para>
<para> <para>
Similarly, <xref linkend="guc-hot-standby-feedback"/> on its own, without Similarly, <xref linkend="guc-hot-standby-feedback"/> on its own, without
also using a replication slot, provides protection against relevant rows also using a replication slot, provides protection against relevant rows
being removed by vacuum, but provides no protection during any time period being removed by vacuum, but provides no protection during any time period
when the standby is not connected. Replication slots overcome these when the standby is not connected.
disadvantages.
</para> </para>
<caution>
<para>
Beware that replication slots can cause the server to retain so
many WAL segments that they fill up the space allocated for
<literal>pg_wal</literal>.
<xref linkend="guc-max-slot-wal-keep-size"/> can be used to limit the size
of WAL files retained by replication slots.
</para>
</caution>
<sect3 id="streaming-replication-slots-manipulation"> <sect3 id="streaming-replication-slots-manipulation">
<title>Querying and Manipulating Replication Slots</title> <title>Querying and Manipulating Replication Slots</title>
<para> <para>