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doc: update "node rejoin" documentation
In particular, update examples to reflect changed output in repmgr 4.3.
This commit is contained in:
Ian Barwick
@@ -216,6 +216,10 @@
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postgres --single -D /var/lib/pgsql/data/ < /dev/null</programlisting>
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</para>
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</tip>
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<para>
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&repmgr; will attempt to verify whether the node can rejoin as-is, or whether
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<command>pg_rewind</command> must be used (see following section).
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</para>
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</refsect1>
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<refsect1 id="repmgr-node-rejoin-pg-rewind" xreflabel="Using pg_rewind">
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@@ -241,65 +245,92 @@
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</para>
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</note>
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<para>
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We strongly recommend familiarizing yourself with <command>pg_rewind</command> before attempting
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to use it with &repmgr;, as while it is an extremely useful tool, it is <emphasis>not</emphasis>
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a "magic bullet".
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</para>
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<para>
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A typical use-case for <command>pg_rewind</command> is when a scenario like the following
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is encountered:
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<programlisting>
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$ repmgr node rejoin -f /etc/repmgr.conf -d 'host=node3 dbname=repmgr user=repmgr' \
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--force-rewind --config-files=postgresql.local.conf,postgresql.conf --verbose --dry-run
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INFO: replication connection to the follow target node was successful
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INFO: local and follow target system identifiers match
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DETAIL: system identifier is 6652184002263212600
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ERROR: this node cannot attach to follow target node 3
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DETAIL: follow target server's timeline 2 forked off current database system timeline 1 before current recovery point 0/610D710
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HINT: use --force-rewind to execute pg_rewind</programlisting>
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Here, <literal>node3</literal> was promoted to a primary while the local node was
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still attached to the previous primary; this can potentially happen during e.g. a
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network split. <command>pg_rewind</command> can re-sync the local node with <literal>node3</literal>,
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removing the need for a full reclone.
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</para>
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<para>
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To have <command>repmgr node rejoin</command> use <command>pg_rewind</command>,
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pass the command line option <literal>--force-rewind</literal>, which will tell &repmgr;
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to execute <command>pg_rewind</command> to ensure the node can be rejoined successfully.
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</para>
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<para>
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Be aware that if <command>pg_rewind</command> is executed and actually performs a
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rewind operation, any configuration files in the PostgreSQL data directory will be
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overwritten with those from the source server.
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</para>
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<para>
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To prevent this happening, provide a comma-separated list of files to retain
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using the <literal>--config-file</literal> command line option; the specified files
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will be archived in a temporary directory (whose parent directory can be specified with
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<literal>--config-archive-dir</literal>) and restored once the rewind operation is
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complete.
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</para>
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<important>
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<para>
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Be aware that if <command>pg_rewind</command> is executed and actually performs a
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rewind operation, any configuration files in the PostgreSQL data directory will be
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overwritten with those from the source server.
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</para>
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<para>
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To prevent this happening, provide a comma-separated list of files to retain
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using the <literal>--config-file</literal> command line option; the specified files
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will be archived in a temporary directory (whose parent directory can be specified with
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<literal>--config-archive-dir</literal>) and restored once the rewind operation is
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complete.
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</para>
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</important>
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<para>
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Example, first using <literal>--dry-run</literal>, then actually executing the
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<literal>node rejoin command</literal>.
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<programlisting>
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$ repmgr node rejoin -f /etc/repmgr.conf -d 'host=node1 dbname=repmgr user=repmgr' \
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--force-rewind --config-files=postgresql.local.conf,postgresql.conf --verbose --dry-run
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NOTICE: using provided configuration file "/etc/repmgr.conf"
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$ repmgr node rejoin -f /etc/repmgr.conf -d 'host=node3 dbname=repmgr user=repmgr' \
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--config-files=postgresql.local.conf,postgresql.conf --verbose --force-rewind --dry-run
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INFO: replication connection to the follow target node was successful
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INFO: local and follow target system identifiers match
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DETAIL: system identifier is 6652460429293670710
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NOTICE: pg_rewind execution required for this node to attach to follow target node 3
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DETAIL: follow target server's timeline 2 forked off current database system timeline 1 before current recovery point 0/610D710
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INFO: prerequisites for using pg_rewind are met
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INFO: file "postgresql.local.conf" would be copied to "/tmp/repmgr-config-archive-node1/postgresql.local.conf"
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INFO: file "postgresql.conf" would be copied to "/tmp/repmgr-config-archive-node1/postgresql.local.conf"
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INFO: 2 files would have been copied to "/tmp/repmgr-config-archive-node1"
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INFO: directory "/tmp/repmgr-config-archive-node1" deleted
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INFO: file "postgresql.local.conf" would be copied to "/tmp/repmgr-config-archive-node2/postgresql.local.conf"
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INFO: file "postgresql.replication-setup.conf" would be copied to "/tmp/repmgr-config-archive-node2/postgresql.replication-setup.conf"
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INFO: pg_rewind would now be executed
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DETAIL: pg_rewind command is:
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pg_rewind -D '/var/lib/postgresql/data' --source-server='host=node1 dbname=repmgr user=repmgr'</programlisting>
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pg_rewind -D '/var/lib/postgresql/data' --source-server='host=node3 dbname=repmgr user=repmgr'
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INFO: prerequisites for executing NODE REJOIN are met</programlisting>
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<note>
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<para>
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If <option>--force-rewind</option> is used with the <option>--dry-run</option> option,
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this checks the prerequisites for using <application>pg_rewind</application>, but cannot
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predict the outcome of actually executing <application>pg_rewind</application>.
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this checks the prerequisites for using <application>pg_rewind</application>, but is
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not an absolute guarantee that actually executing <application>pg_rewind</application>
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will succeed.
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</para>
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</note>
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<programlisting>
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$ repmgr node rejoin -f /etc/repmgr.conf -d 'host=node1 dbname=repmgr user=repmgr' \
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--force-rewind --config-files=postgresql.local.conf,postgresql.conf --verbose
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NOTICE: using provided configuration file "/etc/repmgr.conf"
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INFO: prerequisites for using pg_rewind are met
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INFO: 2 files copied to "/tmp/repmgr-config-archive-node1"
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$ repmgr node rejoin -f /etc/repmgr.conf -d 'host=node3 dbname=repmgr user=repmgr' \
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--config-files=postgresql.local.conf,postgresql.conf --verbose --force-rewind
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NOTICE: pg_rewind execution required for this node to attach to follow target node 3
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DETAIL: follow target server's timeline 2 forked off current database system timeline 1 before current recovery point 0/610D710
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NOTICE: executing pg_rewind
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NOTICE: 2 files copied to /var/lib/pgsql/data
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INFO: directory "/tmp/repmgr-config-archive-node1" deleted
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INFO: deleting "recovery.done"
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INFO: setting node 1's primary to node 2
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NOTICE: starting server using "pg_ctl-l /var/log/postgres/startup.log -w -D '/var/lib/pgsql/data' start"
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waiting for server to start.... done
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server started
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DETAIL: pg_rewind command is "pg_rewind -D '/var/lib/postgresql/data' --source-server='host=node3 dbname=repmgr user=repmgr'"
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NOTICE: 2 files copied to /var/lib/postgresql/data
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NOTICE: setting node 2's upstream to node 3
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NOTICE: starting server using "pg_ctl -l /var/log/postgres/startup.log -w -D '/var/lib/pgsql/data' start"
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NOTICE: NODE REJOIN successful
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DETAIL: node 1 is now attached to node 2</programlisting>
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DETAIL: node 2 is now attached to node 3</programlisting>
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</para>
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</refsect1>
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