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postgres_fdw: Allow postgres_fdw.application_name to include escape sequences.

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application_name that used when postgres_fdw establishes a connection to
a foreign server can be specified in either or both a connection parameter
of a server object and GUC postgres_fdw.application_name. This commit
allows those parameters to include escape sequences that begins with
% character. Then postgres_fdw replaces those escape sequences with
status information. For example, %d and %u are replaced with user name
and database name in local server, respectively. This feature enables us
to add information more easily to track remote transactions or queries,
into application_name of a remote connection.

Author: Hayato Kuroda
Reviewed-by: Kyotaro Horiguchi, Masahiro Ikeda, Hou Zhijie, Fujii Masao
Discussion: https://postgr.es/m/TYAPR01MB5866FAE71C66547C64616584F5EB9@TYAPR01MB5866.jpnprd01.prod.outlook.com
Discussion: https://postgr.es/m/TYCPR01MB5870D1E8B949DAF6D3B84E02F5F29@TYCPR01MB5870.jpnprd01.prod.outlook.com
This commit is contained in:
Fujii Masao
2021-12-24 16:55:11 +09:00
parent 94226d4506
commit 6e0cb3dec1
6 changed files with 218 additions and 1 deletions
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67
doc/src/sgml/postgres-fdw.sgml
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@ -130,6 +130,20 @@
server encoding)
</para>
</listitem>
<listitem>
<para>
<literal>application_name</literal> - this may appear in
<emphasis>either or both</emphasis> a connection and
<xref linkend="guc-pgfdw-application-name"/>.
If both are present, <varname>postgres_fdw.application_name</varname>
overrides the connection setting.
Unlike <application>libpq</application>,
<filename>postgres_fdw</filename> allows
<varname>application_name</varname> to include
<quote>escape sequences</quote>.
See <xref linkend="guc-pgfdw-application-name"/> for details.
</para>
</listitem>
<listitem>
<para>
<literal>fallback_application_name</literal> (always set to
@ -920,7 +934,7 @@ postgres=# SELECT postgres_fdw_disconnect_all();
<title>Configuration Parameters</title>
<variablelist>
<varlistentry>
<varlistentry id="guc-pgfdw-application-name" xreflabel="postgres_fdw.application_name">
<term>
<varname>postgres_fdw.application_name</varname> (<type>string</type>)
<indexterm>
@ -946,6 +960,57 @@ postgres=# SELECT postgres_fdw_disconnect_all();
marks (<literal>?</literal>).
See <xref linkend="guc-application-name"/> for details.
</para>
<para>
<literal>%</literal> characters begin <quote>escape sequences</quote>
that are replaced with status information as outlined below.
Unrecognized escapes are ignored. Other characters are copied straight
to the application name. Note that it's not allowed to specify a
plus/minus sign or a numeric literal after the <literal>%</literal>
and before the option, for alignment and padding.
</para>
<informaltable>
<tgroup cols="2">
<thead>
<row>
<entry>Escape</entry>
<entry>Effect</entry>
</row>
</thead>
<tbody>
<row>
<entry><literal>%a</literal></entry>
<entry>Application name in local server</entry>
</row>
<row>
<entry><literal>%u</literal></entry>
<entry>User name in local server</entry>
</row>
<row>
<entry><literal>%d</literal></entry>
<entry>Database name in local server</entry>
</row>
<row>
<entry><literal>%p</literal></entry>
<entry>Process ID of backend in local server</entry>
</row>
<row>
<entry><literal>%%</literal></entry>
<entry>Literal %</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
For example, suppose user <literal>local_user</literal> establishes
a connection from database <literal>local_db</literal> to
<literal>foreign_db</literal> as user <literal>foreign_user</literal>,
the setting <literal>'db=%d, user=%u'</literal> is replaced with
<literal>'db=local_db, user=local_user'</literal>.
</para>
</listitem>
</varlistentry>
</variablelist>