doc: Add note about the server name of postgres_fdw_get_connections() returns.

Previously the document didn't mention the case where
postgres_fdw_get_connections() returns NULL in server_name column.
Users might be confused about why NULL was returned.

This commit adds the note that, in postgres_fdw_get_connections(),
the server name of an invalid connection will be NULL if the server is dropped.

Suggested-by: Zhijie Hou
Author: Bharath Rupireddy
Reviewed-by: Zhijie Hou, Fujii Masao
Discussion: https://postgr.es/m/e7ddd14e96444fce88e47a709c196537@G08CNEXMBPEKD05.g08.fujitsu.local

diff --git a/doc/src/sgml/postgres-fdw.sgml b/doc/src/sgml/postgres-fdw.sgml
index 6a91926da837cdea8e4e8dcb0bd49592d9df8854..9adc8d12a9dd05f34fddbc0f4efb866ee3fa9d3e 100644 (file)
--- a/doc/src/sgml/postgres-fdw.sgml
+++ b/doc/src/sgml/postgres-fdw.sgml
@@ -493,7 +493,9 @@ OPTIONS (ADD password_required 'false');
       each connection is valid or not. false is returned
       if the foreign server connection is used in the current local
       transaction but its foreign server or user mapping is changed or
-      dropped, and then such invalid connection will be closed at
+      dropped (Note that server name of an invalid connection will be
+      NULL if the server is dropped),
+      and then such invalid connection will be closed at
       the end of that transaction. true is returned
       otherwise. If there are no open connections, no record is returned.
       Example usage of the function: