From eab81953682d5087295afb911c93f36cb1533bd9 Mon Sep 17 00:00:00 2001 From: Etsuro Fujita Date: Tue, 8 Jun 2021 13:45:00 +0900 Subject: [PATCH] Doc: Further update documentation for asynchronous execution. Add a note about asynchronous execution by postgres_fdw when applied to Append nodes that contain synchronous subplan(s) as well. Follow-up for commit 27e1f1456. Andrey Lepikhov and Etsuro Fujita Discussion: https://postgr.es/m/58fa2aa5-07f5-80b5-59a1-fec8a349fee7%40postgrespro.ru --- doc/src/sgml/postgres-fdw.sgml | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/doc/src/sgml/postgres-fdw.sgml b/doc/src/sgml/postgres-fdw.sgml index 65171841c94..5aced083e9e 100644 --- a/doc/src/sgml/postgres-fdw.sgml +++ b/doc/src/sgml/postgres-fdw.sgml @@ -411,6 +411,19 @@ OPTIONS (ADD password_required 'false'); In such a case, it may be more performant to disable this option to eliminate the overhead associated with running queries asynchronously. + + + Asynchronous execution is applied even when an + Append node contains subplan(s) executed + synchronously as well as subplan(s) executed asynchronously. + In such a case, if the asynchronous subplans are ones processed using + postgres_fdw, tuples from the asynchronous + subplans are not returned until after at least one synchronous subplan + returns all tuples, as that subplan is executed while the asynchronous + subplans are waiting for the results of asynchronous queries sent to + foreign servers. + This behavior might change in a future release. +