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Diffstat (limited to 'doc/src/sgml/postgres-fdw.sgml')
| -rw-r--r-- | doc/src/sgml/postgres-fdw.sgml | 46 |
1 files changed, 44 insertions, 2 deletions
diff --git a/doc/src/sgml/postgres-fdw.sgml b/doc/src/sgml/postgres-fdw.sgml index 7c922821e98..5a829d537a6 100644 --- a/doc/src/sgml/postgres-fdw.sgml +++ b/doc/src/sgml/postgres-fdw.sgml @@ -265,6 +265,46 @@ </sect3> <sect3> + <title>Remote Execution Options</title> + + <para> + By default, only <literal>WHERE</> clauses using built-in operators and + functions will be considered for execution on the remote server. Clauses + involving non-built-in functions are checked locally after rows are + fetched. If such functions are available on the remote server and can be + relied on to produce the same results as they do locally, performance can + be improved by sending such <literal>WHERE</> clauses for remote + execution. This behavior can be controlled using the following option: + </para> + + <variablelist> + + <varlistentry> + <term><literal>extensions</literal></term> + <listitem> + <para> + This option is a comma-separated list of names + of <productname>PostgreSQL</> extensions that are installed, in + compatible versions, on both the local and remote servers. Functions + and operators that are immutable and belong to a listed extension will + be considered shippable to the remote server. + This option can only be specified for foreign servers, not per-table. + </para> + </listitem> + </varlistentry> + + </variablelist> + + <para> + When using the <literal>extensions</literal> option, <emphasis>it is the + user's responsibility</> that the listed extensions exist and behave + identically on both the local and remote servers. Otherwise, remote + queries may fail or behave unexpectedly. + </para> + + </sect3> + + <sect3> <title>Updatability Options</title> <para> @@ -427,8 +467,10 @@ execution, and by not retrieving table columns that are not needed for the current query. To reduce the risk of misexecution of queries, <literal>WHERE</> clauses are not sent to the remote server unless they use - only built-in data types, operators, and functions. Operators and - functions in the clauses must be <literal>IMMUTABLE</> as well. + only data types, operators, and functions that are built-in or belong to an + extension that's listed in the foreign server's <literal>extensions</> + option. Operators and functions in such clauses must + be <literal>IMMUTABLE</> as well. </para> <para> |