From 15fcd33e0694428d0567a6796891b759bc91e6f9 Mon Sep 17 00:00:00 2001 From: Etsuro Fujita Date: Mon, 17 May 2021 17:30:00 +0900 Subject: [PATCH] Doc: Update documentation for asynchronous execution. Add a note of caution on the performance of asynchronous execution by postgres_fdw. Follow-up for commit 27e1f1456. Stephen Frost, a little bit expanded by me. Discussion: https://postgr.es/m/20210506171224.GV20766%40tamriel.snowman.net --- doc/src/sgml/postgres-fdw.sgml | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/doc/src/sgml/postgres-fdw.sgml b/doc/src/sgml/postgres-fdw.sgml index 839126c4efe..fb87372bde1 100644 --- a/doc/src/sgml/postgres-fdw.sgml +++ b/doc/src/sgml/postgres-fdw.sgml @@ -401,6 +401,16 @@ OPTIONS (ADD password_required 'false'); A table-level option overrides a server-level option. The default is false. + + + In order to ensure that the data being returned from a foreign server + is consistent, postgres_fdw will only open one + connection for a given foreign server and will run all queries against + that server sequentially even if there are multiple foreign tables + involved, unless those tables are subject to different user mappings. + In such a case, it may be more performant to disable this option to + eliminate the overhead associated with running queries asynchronously. + -- 2.30.2