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Fix some documentation in pg_rewind

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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
This commit is contained in:
Michael Paquier 2019-04-05 10:38:21 +09:00
parent 7dbc0759e0
commit 064b3fcbdb
1 changed files with 30 additions and 4 deletions
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34
doc/src/sgml/ref/pg_rewind.sgml
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@ -153,10 +153,12 @@ PostgreSQL documentation
<listitem>
<para>
Specifies a libpq connection string to connect to the source
<productname>PostgreSQL</productname> server to synchronize the target with.
The connection must be a normal (non-replication) connection
with superuser access. This option requires the source
server to be running and not in recovery mode.
<productname>PostgreSQL</productname> server to synchronize the target
with. The connection must be a normal (non-replication) connection
with a role having sufficient permissions to execute the functions
used by <application>pg_rewind</application> on the source server
(see Notes section for details) or a superuser role. This option
requires the source server to be running and not in recovery mode.
</para>
</listitem>
</varlistentry>
@ -221,6 +223,30 @@ PostgreSQL documentation
<refsect1>
<title>Notes</title>
<para>
When executing <application>pg_rewind</application> using an online
cluster as source, a role having sufficient permissions to execute the
functions used by <application>pg_rewind</application> on the source
cluster can be used instead of a superuser. Here is how to create such
a role, named <literal>rewind_user</literal> here:
<programlisting>
CREATE USER rewind_user LOGIN;
GRANT EXECUTE ON function pg_catalog.pg_ls_dir(text, boolean, boolean) TO rewind_user;
GRANT EXECUTE ON function pg_catalog.pg_stat_file(text, boolean) TO rewind_user;
GRANT EXECUTE ON function pg_catalog.pg_read_binary_file(text) TO rewind_user;
GRANT EXECUTE ON function pg_catalog.pg_read_binary_file(text, bigint, bigint, boolean) TO rewind_user;
</programlisting>
</para>
<para>
When executing <application>pg_rewind</application> using an online
cluster as source which has been recently promoted, it is necessary
to execute a <command>CHECKPOINT</command> after promotion so as its
control file reflects up-to-date timeline information, which is used by
<application>pg_rewind</application> to check if the target cluster
can be rewound using the designated source cluster.
</para>
<refsect2>
<title>How it works</title>