index 9dd52ff275024a1dcbe07e465885f147a77dbcab..236c0af65fba311747a28579e1c07e391a38fab4 100644 (file)
@@ -924,7 +924,8 @@ primary_conninfo = 'host=192.168.1.50 port=5432 user=foo password=foopass'
<secondary>streaming replication</secondary>
</indexterm>
<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,
and that the primary does not remove rows which could cause a
<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
storing the segments in an archive using
<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
- known to be needed. On the other hand, replication slots can 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"/> limits the size of WAL files
- retained by replication slots.
+ known to be needed.
</para>
<para>
Similarly, <xref linkend="guc-hot-standby-feedback"/> on its own, without
also using a replication slot, provides protection against relevant rows
being removed by vacuum, but provides no protection during any time period
- when the standby is not connected. Replication slots overcome these
- disadvantages.
+ when the standby is not connected.
</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">
<title>Querying and Manipulating Replication Slots</title>
<para>