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Commitd4df2bc

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author
Liudmila Mantrova
committed
DOC: improved major node documentation
1 parent53a6668 commitd4df2bc

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‎doc/src/sgml/multimaster.sgml

Lines changed: 34 additions & 17 deletions
Original file line numberDiff line numberDiff line change
@@ -705,21 +705,11 @@ a new winner can be chosen in case of another network failure.
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in a two-node cluster configuration, or to quickly restore a
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single node in a broken cluster.
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</para>
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<important>
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<para>
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If your cluster has more than two nodes, promoting one of the
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nodes to the major status can lead to split-brain problems
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in case of network failures, and reduce the number of possible
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failover options. Consider
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<link linkend="setting-up-a-referee">setting up a standalone referee</link>
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instead.
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</para>
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</important>
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<para>
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To make one of the nodes major, enable the
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<literal>multimaster.major_node</literal> parameter on this node:
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<programlisting>
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ALTER SYSTEM SET multimaster.major_node TO on
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ALTER SYSTEM SET multimaster.major_node TO on;
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SELECT pg_reload_conf();
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</programlisting>
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</para>
@@ -730,6 +720,18 @@ SELECT pg_reload_conf();
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referee for your cluster, the <varname>major_node</varname>
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option is forbidden.
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</para>
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<important>
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<para>
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If your cluster has more than two nodes, do not use the major node
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setting, as it can lead to split-brain problems
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in case of network failures, and reduce the number of possible
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failover options. If the major node gets isolated by a network failure
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while the majority of nodes are connected to each other, both the major
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node and the subset that has a quorum will continue working. Consider
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<link linkend="setting-up-a-referee">setting up a standalone referee</link>
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instead.
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</para>
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</important>
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</sect4>
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</sect3>
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</sect2>
@@ -1085,14 +1087,29 @@ pg_ctl -D <replaceable>datadir</replaceable> -l <replaceable>pg.log</replaceable
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</indexterm>
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</term>
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<listitem>
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<para>The node with this flag continues working even if it cannot access the majority of other nodes.
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This may be required to break the symmetry in two-node clusters.
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<para>The node with this flag continues working even if there is no quorum.
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This may be required to break the symmetry in two-node clusters,
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or to quickly restore a single node in a broken cluster.
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</para>
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<important>
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<para>This parameter should be used with caution. This parameter can cause the
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split-brain problem if you use it on clusters with more than two nodes, or set
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it to <literal>true</literal> on more than one node.
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Only one node in the cluster can be the major node.
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<para>This parameter should be used with caution to avoid split-brain
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problems:
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<itemizedlist>
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<listitem>
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<para>
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Do not use the <parameter>major_node</> parameter on clusters with more
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than two nodes. If the major node gets isolated by a network failure
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while the majority of nodes are connected to each other, both the major
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node and the subset that has a quorum will continue working.
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Consider setting up a standalone referee instead.
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</para>
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</listitem>
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<listitem>
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<para>
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Never set more than one major node in the cluster.
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</para>
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</listitem>
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</itemizedlist>
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</para>
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</important>
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</listitem>

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