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Basically any setting which can contain a user-defined script *must* have the full path set, even if it's repmgr being executed. We could potentially apply some heuristics to detect if the first item in the setting is "repmgr" (or more precisely repmgrd's program name), but this will require some careful thought and testing that it works as intended.
319 lines
15 KiB
Plaintext
319 lines
15 KiB
Plaintext
<appendix id="appendix-faq" xreflabel="FAQ">
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<indexterm>
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<primary>FAQ (Frequently Asked Questions)</primary>
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</indexterm>
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<title>FAQ (Frequently Asked Questions)</title>
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<sect1 id="faq-general" xreflabel="General">
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<title>General</title>
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<sect2 id="faq-xrepmgr-version-diff" xreflabel="Version differences">
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<title>What's the difference between the repmgr versions?</title>
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<para>
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&repmgr; 4 is a complete rewrite of the existing &repmgr; code base
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and implements &repmgr; as a PostgreSQL extension. It
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supports all PostgreSQL versions from 9.3 (although some &repmgr;
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features are not available for PostgreSQL 9.3 and 9.4).
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</para>
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<para>
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&repmgr; 3.x builds on the improved replication facilities added
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in PostgreSQL 9.3, as well as improved automated failover support
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via <application>repmgrd</application>, and is not compatible with PostgreSQL 9.2
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and earlier. We recommend upgrading to &repmgr; 4, as the &repmgr; 3.x
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series will no longer be actively maintained.
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</para>
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<para>
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&repmgr; 2.x supports PostgreSQL 9.0 ~ 9.3. While it is compatible
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with PostgreSQL 9.3, we recommend using repmgr 4.x. &repmgr; 2.x is
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no longer maintained.
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</para>
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</sect2>
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<sect2 id="faq-replication-slots-advantage" xreflabel="Advantages of replication slots">
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<title>What's the advantage of using replication slots?</title>
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<para>
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Replication slots, introduced in PostgreSQL 9.4, ensure that the
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primary server will retain WAL files until they have been consumed
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by all standby servers. This makes WAL file management much easier,
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and if used &repmgr; will no longer insist on a fixed minimum number
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(default: 5000) of WAL files being retained.
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</para>
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<para>
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However this does mean that if a standby is no longer connected to the
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primary, the presence of the replication slot will cause WAL files
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to be retained indefinitely.
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</para>
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</sect2>
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<sect2 id="faq-replication-slots-number" xreflabel="Number of replication slots">
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<title>How many replication slots should I define in <varname>max_replication_slots</varname>?</title>
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<para>
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Normally at least same number as the number of standbys which will connect
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to the node. Note that changes to <varname>max_replication_slots</varname> require a server
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restart to take effect, and as there is no particular penalty for unused
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replication slots, setting a higher figure will make adding new nodes
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easier.
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</para>
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</sect2>
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<sect2 id="faq-hash-index" xreflabel="Hash indexes">
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<title>Does &repmgr; support hash indexes?</title>
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<para>
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Before PostgreSQL 10, hash indexes were not WAL logged and are therefore not suitable
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for use in streaming replication in PostgreSQL 9.6 and earlier. See the
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<ulink url="https://www.postgresql.org/docs/9.6/static/sql-createindex.html#AEN80279">PostgreSQL documentation</ulink>
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for details.
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</para>
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<para>
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From PostgreSQL 10, this restriction has been lifted and hash indexes can be used
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in a streaming replication cluster.
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</para>
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</sect2>
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<sect2 id="faq-upgrades" xreflabel="Upgrading PostgreSQL with repmgr">
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<title>Can &repmgr; assist with upgrading a PostgreSQL cluster?</title>
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<para>
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For <emphasis>minor</emphasis> version upgrades, e.g. from 9.6.7 to 9.6.8, a common
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approach is to upgrade a standby to the latest version, perform a
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<link linkend="performing-switchover">switchover</link> promoting it to a primary,
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then upgrade the former primary.
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</para>
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<para>
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For <emphasis>major</emphasis> version upgrades (e.g. from PostgreSQL 9.6 to PostgreSQL 10),
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the traditional approach is to "reseed" a cluster by upgrading a single
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node with <ulink url="https://www.postgresql.org/docs/current/static/pgupgrade.html">pg_upgrade</ulink>
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and recloning standbys from this.
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</para>
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<para>
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To minimize downtime during major upgrades, for more recent PostgreSQL
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versions (PostgreSQL 9.4 and later),
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<ulink url="https://www.2ndquadrant.com/en/resources/pglogical/">pglogical</ulink>
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can be used to set up a parallel cluster using the newer PostgreSQL version,
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which can be kept in sync with the existing production cluster until the
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new cluster is ready to be put into production.
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</para>
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</sect2>
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<sect2 id="faq-libdir-repmgr-error">
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<title>What does this error mean: <literal>ERROR: could not access file "$libdir/repmgr"</literal>?</title>
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<para>
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It means the &repmgr; extension code is not installed in the
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PostgreSQL application directory. This typically happens when using PostgreSQL
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packages provided by a third-party vendor, which often have different
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filesystem layouts.
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</para>
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<para>
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Either use PostgreSQL packages provided by the community or 2ndQuadrant; if this
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is not possible, contact your vendor for assistance.
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</para>
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</sect2>
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</sect1>
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<sect1 id="faq-repmgr" xreflabel="repmgr">
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<title><command>repmgr</command></title>
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<sect2 id="faq-register-existing-node" xreflabel="registering an existing node">
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<title>Can I register an existing PostgreSQL server with repmgr?</title>
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<para>
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Yes, any existing PostgreSQL server which is part of the same replication
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cluster can be registered with &repmgr;. There's no requirement for a
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standby to have been cloned using &repmgr;.
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</para>
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</sect2>
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<sect2 id="faq-repmgr-clone-other-source" >
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<title>Can I use a standby not cloned by &repmgr; as a &repmgr; node?</title>
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<para>
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For a standby which has been manually cloned or recovered from an external
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backup manager such as Barman, the command
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<command><link linkend="repmgr-standby-clone">repmgr standby clone --recovery-conf-only</link></command>
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can be used to create the correct <filename>recovery.conf</filename> file for
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use with &repmgr; (and will create a replication slot if required). Once this has been done,
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<link linkend="repmgr-standby-register">register the node</link> as usual.
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</para>
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</sect2>
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<sect2 id="faq-repmgr-recovery-conf" >
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<title>What does &repmgr; write in <filename>recovery.conf</filename>, and what options can be set there?</title>
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<para>
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See section <link linkend="repmgr-standby-clone-recovery-conf">Customising recovery.conf</link>.
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</para>
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</sect2>
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<sect2 id="faq-repmgr-failed-primary-standby" xreflabel="Reintegrate a failed primary as a standby">
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<title>How can a failed primary be re-added as a standby?</title>
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<para>
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This is a two-stage process. First, the failed primary's data directory
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must be re-synced with the current primary; secondly the failed primary
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needs to be re-registered as a standby.
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</para>
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<para>
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It's possible to use <command>pg_rewind</command> to re-synchronise the existing data
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directory, which will usually be much
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faster than re-cloning the server. However <command>pg_rewind</command> can only
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be used if PostgreSQL either has <varname>wal_log_hints</varname> enabled, or
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data checksums were enabled when the cluster was initialized.
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</para>
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<para>
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Note that <command>pg_rewind</command> is available as part of the core PostgreSQL
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distribution from PostgreSQL 9.5, and as a third-party utility for PostgreSQL 9.3 and 9.4.
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</para>
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<para>
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&repmgr; provides the command <command>repmgr node rejoin</command> which can
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optionally execute <command>pg_rewind</command>; see the <xref linkend="repmgr-node-rejoin">
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documentation for details, in particular the section <xref linkend="repmgr-node-rejoin-pg-rewind">.
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</para>
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<para>
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If <command>pg_rewind</command> cannot be used, then the data directory will need
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to be re-cloned from scratch.
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</para>
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</sect2>
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<sect2 id="faq-repmgr-check-configuration" xreflabel="Check PostgreSQL configuration">
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<title>Is there an easy way to check my primary server is correctly configured for use with &repmgr;?</title>
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<para>
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Execute <command><link linkend="repmgr-standby-clone">repmgr standby clone</link></command>
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with the <literal>--dry-run</literal> option; this will report any configuration problems
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which need to be rectified.
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</para>
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</sect2>
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<sect2 id="faq-repmgr-clone-skip-config-files" xreflabel="">
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<title>When cloning a standby, how can I get &repmgr; to copy
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<filename>postgresql.conf</filename> and <filename>pg_hba.conf</filename> from the PostgreSQL configuration
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directory in <filename>/etc</filename>?</title>
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<para>
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Use the command line option <literal>--copy-external-config-files</literal>. For more details
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see <xref linkend="repmgr-standby-clone-config-file-copying">.
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</para>
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</sect2>
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<sect2 id="faq-repmgr-shared-preload-libaries-no-repmgrd" xreflabel="shared_preload_libraries without repmgrd">
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<title>Do I need to include <literal>shared_preload_libraries = 'repmgr'</literal>
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in <filename>postgresql.conf</filename> if I'm not using <application>repmgrd</application>?</title>
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<para>
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No, the <literal>repmgr</literal> shared library is only needed when running <application>repmgrd</application>.
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If you later decide to run <application>repmgrd</application>, you just need to add
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<literal>shared_preload_libraries = 'repmgr'</literal> and restart PostgreSQL.
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</para>
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</sect2>
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<sect2 id="faq-repmgr-permissions" xreflabel="Replication permission problems">
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<title>I've provided replication permission for the <literal>repmgr</literal> user in <filename>pg_hba.conf</filename>
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but <command>repmgr</command>/<application>repmgrd</application> complains it can't connect to the server... Why?</title>
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<para>
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<command>repmgr</command> and <application>repmgrd</application> need to be able to connect to the repmgr database
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with a normal connection to query metadata. The <literal>replication</literal> connection
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permission is for PostgreSQL's streaming replication (and doesn't necessarily need to be the <literal>repmgr</literal> user).
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</para>
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</sect2>
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<sect2 id="faq-repmgr-clone-provide-primary-conninfo" xreflabel="Providing primary connection parameters">
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<title>When cloning a standby, why do I need to provide the connection parameters
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for the primary server on the command line, not in the configuration file?</title>
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<para>
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Cloning a standby is a one-time action; the role of the server being cloned
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from could change, so fixing it in the configuration file would create
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confusion. If &repmgr; needs to establish a connection to the primary
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server, it can retrieve this from the <literal>repmgr.nodes</literal> table on the local
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node, and if necessary scan the replication cluster until it locates the active primary.
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</para>
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</sect2>
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<sect2 id="faq-repmgr-clone-waldir-xlogdir" xreflabel="Providing a custom WAL directory">
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<title>When cloning a standby, how do I ensure the WAL files are placed in a custom directory?</title>
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<para>
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Provide the option <literal>--waldir</literal> (<literal>--xlogdir</literal> in PostgreSQL 9.6
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and earlier) with the absolute path to the WAL directory in <varname>pg_basebackup_options</varname>.
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For more details see <xref linkend="cloning-advanced-pg-basebackup-options">.
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</para>
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</sect2>
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<sect2 id="faq-repmgr-events-no-fkey" xreflabel="No foreign key on node_id in repmgr.events">
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<title>Why is there no foreign key on the <literal>node_id</literal> column in the <literal>repmgr.events</literal>
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table?</title>
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<para>
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Under some circumstances event notifications can be generated for servers
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which have not yet been registered; it's also useful to retain a record
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of events which includes servers removed from the replication cluster
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which no longer have an entry in the <literal>repmrg.nodes</literal> table.
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</para>
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</sect2>
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</sect1>
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<sect1 id="faq-repmgrd" xreflabel="repmgrd">
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<title><application>repmgrd</application></title>
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<sect2 id="faq-repmgrd-prevent-promotion" xreflabel="Prevent standby from being promoted to primary">
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<title>How can I prevent a node from ever being promoted to primary?</title>
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<para>
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In `repmgr.conf`, set its priority to a value of 0 or less; apply the changed setting with
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<command><link linkend="repmgr-standby-register">repmgr standby register --force</link></command>.
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</para>
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<para>
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Additionally, if <varname>failover</varname> is set to <literal>manual</literal>, the node will never
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be considered as a promotion candidate.
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</para>
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</sect2>
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<sect2 id="faq-repmgrd-delayed-standby" xreflabel="Delayed standby support">
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<title>Does <application>repmgrd</application> support delayed standbys?</title>
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<para>
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<application>repmgrd</application> can monitor delayed standbys - those set up with
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<varname>recovery_min_apply_delay</varname> set to a non-zero value
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in <filename>recovery.conf</filename> - but as it's not currently possible
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to directly examine the value applied to the standby, <application>repmgrd</application>
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may not be able to properly evaluate the node as a promotion candidate.
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</para>
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<para>
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We recommend that delayed standbys are explicitly excluded from promotion
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by setting <varname>priority</varname> to <literal>0</literal> in
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<filename>repmgr.conf</filename>.
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</para>
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<para>
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Note that after registering a delayed standby, <application>repmgrd</application> will only start
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once the metadata added in the primary node has been replicated.
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</para>
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</sect2>
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<sect2 id="faq-repmgrd-logfile-rotate" xreflabel="repmgrd logfile rotation">
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<title>How can I get <application>repmgrd</application> to rotate its logfile?</title>
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<para>
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Configure your system's <literal>logrotate</literal> service to do this; see <xref linkend="repmgrd-log-rotation">.
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</para>
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</sect2>
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<sect2 id="faq-repmgrd-recloned-no-start" xreflabel="repmgrd not restarting after node cloned">
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<title>I've recloned a failed primary as a standby, but <application>repmgrd</application> refuses to start?</title>
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<para>
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Check you registered the standby after recloning. If unregistered, the standby
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cannot be considered as a promotion candidate even if <varname>failover</varname> is set to
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<literal>automatic</literal>, which is probably not what you want. <application>repmgrd</application> will start if
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<varname>failover</varname> is set to <literal>manual</literal> so the node's replication status can still
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be monitored, if desired.
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</para>
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</sect2>
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<sect2 id="faq-repmgrd-pg-bindir" xreflabel="repmgrd does not apply pg_bindir to promote_command or follow_command">
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<title>
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<application>repmgrd</application> ignores pg_bindir when executing <varname>promote_command</varname> or <varname>follow_command</varname>
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</title>
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<para>
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<varname>promote_command</varname> or <varname>follow_command</varname> can be user-defined scripts,
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so &repmgr; will not apply <option>pg_bindir</option> even if excuting &repmgr;. Always provide the full
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path; see <xref linkend="repmgrd-automatic-failover-configuration"> for more details.
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</para>
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</sect2>
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</sect1>
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</appendix>
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