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Add docs about postgres_fdw's setting of search_path and other GUCs.

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This behavior wasn't documented, but it should be because it's user-visible
in triggers and other functions executed on the remote server.
Per question from Adam Fuchs.

Back-patch to 9.3 where postgres_fdw was added.
This commit is contained in:
Tom Lane 2015-08-15 14:31:04 -04:00
parent 5869cbfef4
commit 522400a519
1 changed files with 35 additions and 0 deletions
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35
doc/src/sgml/postgres-fdw.sgml
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@ -437,6 +437,41 @@
</para>
</sect2>
<sect2>
<title>Remote Query Execution Environment</title>
<para>
In the remote sessions opened by <filename>postgres_fdw</>,
the <xref linkend="guc-search-path"> parameter is set to
just <literal>pg_catalog</>, so that only built-in objects are visible
without schema qualification. This is not an issue for queries
generated by <filename>postgres_fdw</> itself, because it always
supplies such qualification. However, this can pose a hazard for
functions that are executed on the remote server via triggers or rules
on remote tables. For example, if a remote table is actually a view,
any functions used in that view will be executed with the restricted
search path. It is recommended to schema-qualify all names in such
functions, or else attach <literal>SET search_path</> options
(see <xref linkend="sql-createfunction">) to such functions
to establish their expected search path environment.
</para>
<para>
<filename>postgres_fdw</> likewise establishes remote session settings
for the parameters <xref linkend="guc-timezone">,
<xref linkend="guc-datestyle">, <xref linkend="guc-intervalstyle">,
and <xref linkend="guc-extra-float-digits">. These are less likely
to be problematic than <varname>search_path</>, but can be handled
with function <literal>SET</> options if the need arises.
</para>
<para>
It is <emphasis>not</> recommended that you override this behavior by
changing the session-level settings of these parameters; that is likely
to cause <filename>postgres_fdw</> to malfunction.
</para>
</sect2>
<sect2>
<title>Cross-Version Compatibility</title>