From c522b63967f97d4c8fd54f6ebbd0db557d6b40d9 Mon Sep 17 00:00:00 2001 From: Bharath Rupireddy Date: Mon, 23 Nov 2020 11:59:32 +0530 Subject: [PATCH v1] postgre_fdw connection cache discard tests and documentation This patch adds the tests and documentation related to connection cache discard feature. --- .../postgres_fdw/expected/postgres_fdw.out | 152 +++++++++++++++++- contrib/postgres_fdw/sql/postgres_fdw.sql | 87 ++++++++++ doc/src/sgml/postgres-fdw.sgml | 117 ++++++++++++++ 3 files changed, 355 insertions(+), 1 deletion(-) diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out index 2d88d06358..ded26388e6 100644 --- a/contrib/postgres_fdw/expected/postgres_fdw.out +++ b/contrib/postgres_fdw/expected/postgres_fdw.out @@ -8911,7 +8911,7 @@ DO $d$ END; $d$; ERROR: invalid option "password" -HINT: Valid options in this context are: service, passfile, channel_binding, connect_timeout, dbname, host, hostaddr, port, options, application_name, keepalives, keepalives_idle, keepalives_interval, keepalives_count, tcp_user_timeout, sslmode, sslcompression, sslcert, sslkey, sslrootcert, sslcrl, requirepeer, ssl_min_protocol_version, ssl_max_protocol_version, gssencmode, krbsrvname, gsslib, target_session_attrs, use_remote_estimate, fdw_startup_cost, fdw_tuple_cost, extensions, updatable, fetch_size +HINT: Valid options in this context are: service, passfile, channel_binding, connect_timeout, dbname, host, hostaddr, port, options, application_name, keepalives, keepalives_idle, keepalives_interval, keepalives_count, tcp_user_timeout, sslmode, sslcompression, sslcert, sslkey, sslrootcert, sslcrl, requirepeer, ssl_min_protocol_version, ssl_max_protocol_version, gssencmode, krbsrvname, gsslib, target_session_attrs, use_remote_estimate, fdw_startup_cost, fdw_tuple_cost, extensions, updatable, fetch_size, keep_connection CONTEXT: SQL statement "ALTER SERVER loopback_nopw OPTIONS (ADD password 'dummypw')" PL/pgSQL function inline_code_block line 3 at EXECUTE -- If we add a password for our user mapping instead, we should get a different @@ -9035,3 +9035,153 @@ ERROR: 08006 COMMIT; -- Clean up DROP PROCEDURE terminate_backend_and_wait(text); +-- =================================================================== +-- disconnect connections that are cached/kept by the local session +-- =================================================================== +-- Change application names of remote connections to special ones so that we +-- can easily check for their existence. +ALTER SERVER loopback OPTIONS (SET application_name 'fdw_disconnect_cached_conn_1'); +ALTER SERVER loopback2 OPTIONS (application_name 'fdw_disconnect_cached_conn_2'); +-- By default, the connections associated with foreign server are cached i.e. +-- keep_connection option is on. Set it to off. +ALTER SERVER loopback OPTIONS (keep_connection 'off'); +-- Connection related to loopback server is closed by the local session at the +-- end of xact as the keep_connection was set to off. +SELECT 1 FROM ft1 LIMIT 1; + ?column? +---------- + 1 +(1 row) + +-- Connection should not exist. +SELECT application_name FROM pg_stat_activity + WHERE application_name = 'fdw_disconnect_cached_conn_1'; + application_name +------------------ +(0 rows) + +-- Connection related to loopback2 server is cached by the local session as the +-- keep_connection is on. +SELECT 1 FROM ft6 LIMIT 1; + ?column? +---------- + 1 +(1 row) + +-- Connection should exist. +SELECT application_name FROM pg_stat_activity + WHERE application_name = 'fdw_disconnect_cached_conn_2'; + application_name +------------------------------ + fdw_disconnect_cached_conn_2 +(1 row) + +-- By default, keep_connections GUC is on i.e. local session caches all the +-- foreign server connections that are made. +SHOW postgres_fdw.keep_connections; + postgres_fdw.keep_connections +------------------------------- + on +(1 row) + +-- Set it off i.e. the cached connections which are used after this setting are +-- disconnected at the end of respective xacts. +SET postgres_fdw.keep_connections TO off; +-- Connection related to loopback2 server are closed at the end of xact. +SELECT 1 FROM ft6 LIMIT 1; + ?column? +---------- + 1 +(1 row) + +-- Connection should not exist. +SELECT application_name FROM pg_stat_activity + WHERE application_name = 'fdw_disconnect_cached_conn_2'; + application_name +------------------ +(0 rows) + +-- Connections from hereafter are cached. +SET postgres_fdw.keep_connections TO on; +-- Connection related to loopback server is cached. +ALTER SERVER loopback OPTIONS (SET keep_connection 'on'); +-- Connections related to loopback and loopback2 are cached. +SELECT 1 FROM ft1 LIMIT 1; + ?column? +---------- + 1 +(1 row) + +SELECT 1 FROM ft6 LIMIT 1; + ?column? +---------- + 1 +(1 row) + +-- Connection related to loopback server is disconnected. Connection related to +-- loopback2 server still exists. +SELECT postgres_fdw_disconnect('loopback'); + postgres_fdw_disconnect +------------------------- + t +(1 row) + +-- Connection should not exist. +SELECT application_name FROM pg_stat_activity + WHERE application_name = 'fdw_disconnect_cached_conn_1'; + application_name +------------------ +(0 rows) + +-- Connection should exist. +SELECT application_name FROM pg_stat_activity + WHERE application_name = 'fdw_disconnect_cached_conn_2'; + application_name +------------------------------ + fdw_disconnect_cached_conn_2 +(1 row) + +-- Make loopback server connection again. Now, both loopback and loopback2 +-- server connections exist in the local session. +SELECT 1 FROM ft1 LIMIT 1; + ?column? +---------- + 1 +(1 row) + +-- Connection should exist. +SELECT application_name FROM pg_stat_activity + WHERE application_name = 'fdw_disconnect_cached_conn_1'; + application_name +------------------------------ + fdw_disconnect_cached_conn_1 +(1 row) + +-- Discard all the connections i.e. connections related to loopback and +-- loopback2 server. +SELECT postgres_fdw_disconnect(); + postgres_fdw_disconnect +------------------------- + t +(1 row) + +-- Both the connections should not exist. +SELECT application_name FROM pg_stat_activity + WHERE application_name = 'fdw_disconnect_cached_conn_1'; + application_name +------------------ +(0 rows) + +SELECT application_name FROM pg_stat_activity + WHERE application_name = 'fdw_disconnect_cached_conn_2'; + application_name +------------------ +(0 rows) + +-- The server name provided doesn't exist, so false is returned. +SELECT postgres_fdw_disconnect('unknownserver'); + postgres_fdw_disconnect +------------------------- + f +(1 row) + diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql index 7581c5417b..a2b3e53bba 100644 --- a/contrib/postgres_fdw/sql/postgres_fdw.sql +++ b/contrib/postgres_fdw/sql/postgres_fdw.sql @@ -2697,3 +2697,90 @@ COMMIT; -- Clean up DROP PROCEDURE terminate_backend_and_wait(text); + +-- =================================================================== +-- disconnect connections that are cached/kept by the local session +-- =================================================================== + +-- Change application names of remote connections to special ones so that we +-- can easily check for their existence. +ALTER SERVER loopback OPTIONS (SET application_name 'fdw_disconnect_cached_conn_1'); +ALTER SERVER loopback2 OPTIONS (application_name 'fdw_disconnect_cached_conn_2'); + +-- By default, the connections associated with foreign server are cached i.e. +-- keep_connection option is on. Set it to off. +ALTER SERVER loopback OPTIONS (keep_connection 'off'); + +-- Connection related to loopback server is closed by the local session at the +-- end of xact as the keep_connection was set to off. +SELECT 1 FROM ft1 LIMIT 1; + +-- Connection should not exist. +SELECT application_name FROM pg_stat_activity + WHERE application_name = 'fdw_disconnect_cached_conn_1'; + +-- Connection related to loopback2 server is cached by the local session as the +-- keep_connection is on. +SELECT 1 FROM ft6 LIMIT 1; + +-- Connection should exist. +SELECT application_name FROM pg_stat_activity + WHERE application_name = 'fdw_disconnect_cached_conn_2'; + +-- By default, keep_connections GUC is on i.e. local session caches all the +-- foreign server connections that are made. +SHOW postgres_fdw.keep_connections; + +-- Set it off i.e. the cached connections which are used after this setting are +-- disconnected at the end of respective xacts. +SET postgres_fdw.keep_connections TO off; + +-- Connection related to loopback2 server are closed at the end of xact. +SELECT 1 FROM ft6 LIMIT 1; + +-- Connection should not exist. +SELECT application_name FROM pg_stat_activity + WHERE application_name = 'fdw_disconnect_cached_conn_2'; + +-- Connections from hereafter are cached. +SET postgres_fdw.keep_connections TO on; + +-- Connection related to loopback server is cached. +ALTER SERVER loopback OPTIONS (SET keep_connection 'on'); + +-- Connections related to loopback and loopback2 are cached. +SELECT 1 FROM ft1 LIMIT 1; +SELECT 1 FROM ft6 LIMIT 1; + +-- Connection related to loopback server is disconnected. Connection related to +-- loopback2 server still exists. +SELECT postgres_fdw_disconnect('loopback'); + +-- Connection should not exist. +SELECT application_name FROM pg_stat_activity + WHERE application_name = 'fdw_disconnect_cached_conn_1'; + +-- Connection should exist. +SELECT application_name FROM pg_stat_activity + WHERE application_name = 'fdw_disconnect_cached_conn_2'; + +-- Make loopback server connection again. Now, both loopback and loopback2 +-- server connections exist in the local session. +SELECT 1 FROM ft1 LIMIT 1; + +-- Connection should exist. +SELECT application_name FROM pg_stat_activity + WHERE application_name = 'fdw_disconnect_cached_conn_1'; + +-- Discard all the connections i.e. connections related to loopback and +-- loopback2 server. +SELECT postgres_fdw_disconnect(); + +-- Both the connections should not exist. +SELECT application_name FROM pg_stat_activity + WHERE application_name = 'fdw_disconnect_cached_conn_1'; +SELECT application_name FROM pg_stat_activity + WHERE application_name = 'fdw_disconnect_cached_conn_2'; + +-- The server name provided doesn't exist, so false is returned. +SELECT postgres_fdw_disconnect('unknownserver'); diff --git a/doc/src/sgml/postgres-fdw.sgml b/doc/src/sgml/postgres-fdw.sgml index e6fd2143c1..0c9f62e49a 100644 --- a/doc/src/sgml/postgres-fdw.sgml +++ b/doc/src/sgml/postgres-fdw.sgml @@ -477,6 +477,97 @@ OPTIONS (ADD password_required 'false'); + + + Connection Management Options + + + By default the foreign server connections made with + postgres_fdw are kept in local session for re-use. + This may be overridden using the following + option: + + + + + + keep_connection + + + This option controls whether postgres_fdw keeps the + server connection that is made with a specific foreign server. It can be + specified for a foreign server. Default is on. When + set to off, the associated foreign server connection + is discarded at the end of the transaction. + + + + + + + + + + + + Functions + + + postgres_fdw_disconnect ( servername text ) + which takes foreign server name as input. When called in the local session, + it discards the connection previously made to the foreign server and + returns true. If there is no associated connection exists + for the given foreign server, then false is returned. + + + + postgres_fdw_disconnect ( ) which takes no input. + When called in the local session, it discards all the connections + previously made to the foreign servers and returns true. + If there are no previous connections kept by the local session, then + false is returned. + + + + + + Configuration Parameters + + + + + + postgres_fdw.keep_connections (boolean) + + postgres_fdw.keep_connections configuration parameter + + + + + + + Allows postgres_fdw to keep or discard the + connection made to the foreign server by the local session. Default is + on. When set to off the local + session doesn't keep the connections made to the foreign servers. Each + connection is discarded at the end of transaction in which it is used. + + + + Note that when postgres_fdw.keep_connections is set to + off, postgres_fdw discards either the connections + that are made previously and will be used by the local session or the + connections that will be made newly. But the connections that are made + previously and kept, but not used after this parameter is set to off, are + not discarded. To discard them, use + postgres_fdw_disconnect function. + + + + + + + @@ -490,6 +581,32 @@ OPTIONS (ADD password_required 'false'); multiple user identities (user mappings) are used to access the foreign server, a connection is established for each user mapping. + + + Since the postgres_fdw keeps the connections to remote + servers in the local session, the corresponding sessions that are opened on + the remote servers are kept idle until they are re-used by the local session. + This may waste resources if those connections are not frequently used by the + local session. To address this, the postgres_fdw + provides following ways to remove the connections to the remote servers and + so the remote sessions: + + A server level option, keep_connection that is used with + . Default being on, + when set to off the local session doesn't keep remote + connection associated with the foreign server. The connection is + discarded at the end of the transaction. + + A GUC, postgres_fdw.keep_connections, default being + on, when set to off, the local session + doesn't keep remote connections that are made to the foreign servers. Each + connection is discarded at the end of transaction in which it is used. + + postgres_fdw_disconnect() to discard all the + connections or postgres_fdw_disconnect(text) + to discard the connection associated with the given foreign server name. + + -- 2.25.1