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76 lines
3.9 KiB
Plaintext
76 lines
3.9 KiB
Plaintext
<chapter id="promoting-standby" xreflabel="Promoting a standby">
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<title>Promoting a standby server with repmgr</title>
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<para>
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If a primary server fails or needs to be removed from the replication cluster,
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a new primary server must be designated, to ensure the cluster continues
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to function correctly. This can be done with <xref linkend="repmgr-standby-promote">,
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which promotes the standby on the current server to primary.
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</para>
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<para>
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To demonstrate this, set up a replication cluster with a primary and two attached
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standby servers so that the cluster looks like this:
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<programlisting>
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$ repmgr -f /etc/repmgr.conf cluster show
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ID | Name | Role | Status | Upstream | Location | Connection string
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----+-------+---------+-----------+----------+----------+--------------------------------------
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1 | node1 | primary | * running | | default | host=node1 dbname=repmgr user=repmgr
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2 | node2 | standby | running | node1 | default | host=node2 dbname=repmgr user=repmgr
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3 | node3 | standby | running | node1 | default | host=node3 dbname=repmgr user=repmgr</programlisting>
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</para>
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<para>
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Stop the current primary with e.g.:
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<programlisting>
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$ pg_ctl -D /var/lib/postgresql/data -m fast stop</programlisting>
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</para>
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<para>
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At this point the replication cluster will be in a partially disabled state, with
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both standbys accepting read-only connections while attempting to connect to the
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stopped primary. Note that the &repmgr; metadata table will not yet have been updated;
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executing <xref linkend="repmgr-cluster-show"> will note the discrepancy:
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<programlisting>
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$ repmgr -f /etc/repmgr.conf cluster show
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ID | Name | Role | Status | Upstream | Location | Connection string
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----+-------+---------+---------------+----------+----------+--------------------------------------
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1 | node1 | primary | ? unreachable | | default | host=node1 dbname=repmgr user=repmgr
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2 | node2 | standby | running | node1 | default | host=node2 dbname=repmgr user=repmgr
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3 | node3 | standby | running | node1 | default | host=node3 dbname=repmgr user=repmgr
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WARNING: following issues were detected
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node "node1" (ID: 1) is registered as an active primary but is unreachable</programlisting>
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</para>
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<para>
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Now promote the first standby with:
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<programlisting>
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$ repmgr -f /etc/repmgr.conf standby promote</programlisting>
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</para>
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<para>
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This will produce output similar to the following:
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<programlisting>
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INFO: connecting to standby database
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NOTICE: promoting standby
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DETAIL: promoting server using "pg_ctl -l /var/log/postgresql/startup.log -w -D '/var/lib/postgresql/data' promote"
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server promoting
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INFO: reconnecting to promoted server
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NOTICE: STANDBY PROMOTE successful
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DETAIL: node 2 was successfully promoted to primary</programlisting>
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</para>
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<para>
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Executing <xref linkend="repmgr-cluster-show"> will show the current state; as there is now an
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active primary, the previous warning will not be displayed:
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<programlisting>
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$ repmgr -f /etc/repmgr.conf cluster show
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ID | Name | Role | Status | Upstream | Location | Connection string
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----+-------+---------+-----------+----------+----------+--------------------------------------
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1 | node1 | primary | - failed | | default | host=node1 dbname=repmgr user=repmgr
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2 | node2 | primary | * running | | default | host=node2 dbname=repmgr user=repmgr
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3 | node3 | standby | running | node1 | default | host=node3 dbname=repmgr user=repmgr</programlisting>
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</para>
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<para>
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However the sole remaining standby (<literal>node3</literal>) is still trying to replicate from the failed
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primary; <xref linkend="repmgr-standby-follow"> must now be executed to rectify this situation
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(see <xref linkend="follow-new-primary"> for example).
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</para>
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</chapter>
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