From dd1a9544d30f9cb1c3a3a0c3bb1d8dcfb615af08 Mon Sep 17 00:00:00 2001
From: Fujii Masao <fujii@postgresql.org>
Date: Tue, 13 Aug 2024 11:10:18 +0900
Subject: [PATCH v1] doc: Add note on postgres_fdw cross-version compatibility
 limitations.

The documentation mentions that postgres_fdw can be used with remote
servers dating back to PostgreSQL 8.3. However, when using PostgreSQL 9.4
or earlier as a remote server, INSERT ON CONFLICT on a foreign table fails
because this feature is only supported in version 9.5 and later.

This commit adds a note clarifying that when executing INSERT statements
with an ON CONFLICT DO NOTHING clause on a foreign table, the remote
server must be running PostgreSQL 9.5 or later, as earlier versions do not
support this feature.

Back-patch to all supported versions.

Discussion: https://postgr.es/m/47801526-d017-4c89-9f52-c02c449a139b@oss.nttdata.com
---
 doc/src/sgml/postgres-fdw.sgml | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/doc/src/sgml/postgres-fdw.sgml b/doc/src/sgml/postgres-fdw.sgml
index 90969f63ca..468724e94e 100644
--- a/doc/src/sgml/postgres-fdw.sgml
+++ b/doc/src/sgml/postgres-fdw.sgml
@@ -1096,7 +1096,10 @@ postgres=# SELECT postgres_fdw_disconnect_all();
   <para>
    <filename>postgres_fdw</filename> can be used with remote servers dating back
    to <productname>PostgreSQL</productname> 8.3.  Read-only capability is available
-   back to 8.1.  A limitation however is that <filename>postgres_fdw</filename>
+   back to 8.1.
+  </para>
+  <para>
+   A limitation however is that <filename>postgres_fdw</filename>
    generally assumes that immutable built-in functions and operators are
    safe to send to the remote server for execution, if they appear in a
    <literal>WHERE</literal> clause for a foreign table.  Thus, a built-in
@@ -1108,6 +1111,13 @@ postgres=# SELECT postgres_fdw_disconnect_all();
    optimization fence, and placing the problematic function or operator
    outside the sub-<literal>SELECT</literal>.
   </para>
+  <para>
+   Another limitation is that when executing <command>INSERT</command>
+   statements with an <literal>ON CONFLICT DO NOTHING</literal> clause on
+   a foreign table, the remote server must be running
+   <productname>PostgreSQL</productname> 9.5 or later,
+   as earlier versions do not support this feature.
+  </para>
  </sect2>
 
  <sect2 id="postgres-fdw-wait-events">
-- 
2.45.2