8000 Fix some documentation in pg_rewind · postgrespro/postgres_cluster@bfc8068 · GitHub
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michaelpqmichaelpq
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Fix some documentation in pg_rewind
Since 11, it is possible to use a non-superuser role when using an online source cluster with pg_rewind as long as the role has proper permissions to execute on the source all the functions used by pg_rewind, and the documentation stated that a superuser is necessary. Let's add at the same time all the details needed to create such a role. A second confusion which comes a lot from users is that it is necessary to issue a checkpoint on a freshly-promoted standby so as its control file has up-to-date timeline information which is used by pg_rewind to validate the operation. Let's document that properly. This is back-patched down to 9.5 where pg_rewind has been introduced. Author: Michael Paquier Reviewed-by: Magnus Hagander Discussion: https://postgr.es/m/CABUevEz5bpvbwVsYCaSMV80CBZ5-82nkMzbb+Bu=h1m=rLdn=g@mail.gmail.com Backpatch-through: 9.5
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‎doc/src/sgml/ref/pg_rewind.sgml‎

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@@ -155,10 +155,12 @@ PostgreSQL documentation
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<listitem>
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<para>
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Specifies a libpq connection string to connect to the source
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<productname>PostgreSQL</productname> server to synchronize the target with.
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The connection must be a normal (non-replication) connection
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with superuser access. This option requires the source
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server to be running and not in recovery mode.
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<productname>PostgreSQL</productname> server to synchronize the target
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with. The connection must be a normal (non-replication) connection
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with a role having sufficient permissions to execute the functions
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used by <application>pg_rewind</application> on the source server
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(see Notes section for details) or a superuser role. This option
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requires the source server to be running and not in recovery mode.
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</para>
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</listitem>
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</varlistentry>
@@ -246,6 +248,30 @@ PostgreSQL documentation
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<refsect1>
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<title>Notes</title>
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<para>
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When executing <application>pg_rewind</application> using an online
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cluster as source, a role having sufficient permissions to execute the
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functions used by <application>pg_rewind</application> on the source
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cluster can be used instead of a superuser. Here is how to create such
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a role, named <literal>rewind_user</literal> here:
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<programlisting>
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CREATE USER rewind_user LOGIN;
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GRANT EXECUTE ON function pg_catalog.pg_ls_dir(text, boolean, boolean) TO rewind_user;
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GRANT EXECUTE ON function pg_catalog.pg_stat_file(text, boolean) TO rewind_user;
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GRANT EXECUTE ON function pg_catalog.pg_read_binary_file(text) TO rewind_user;
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GRANT EXECUTE ON function pg_catalog.pg_read_binary_file(text, bigint, bigint, boolean) TO rewind_user;
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</programlisting>
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</para>
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<para>
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When executing <application>pg_rewind</application> using an online
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cluster as source which has been recently promoted, it is necessary
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to execute a <command>CHECKPOINT</command> after promotion so as its
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control file reflects up-to-date timeline information, which is used by
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<application>pg_rewind</application> to check if the target cluster
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can be rewound using the designated source cluster.
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</para>
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<refsect2>
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<title>How it works</title>
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