From 13eccc4c4c4b2ac4548608f37b3518160e8f3283 Mon Sep 17 00:00:00 2001 From: Bharath Rupireddy Date: Fri, 1 Jan 2021 14:33:41 +0530 Subject: [PATCH v7 2/3] postgres_fdw add keep_connections GUC to not cache connections This patch adds a new GUC postgres_fdw.keep_connections, default being on, when set to off no remote connections are cached by the local session. --- contrib/postgres_fdw/connection.c | 12 +++-- .../postgres_fdw/expected/postgres_fdw.out | 50 +++++++++++++++++++ contrib/postgres_fdw/postgres_fdw.c | 16 ++++++ contrib/postgres_fdw/postgres_fdw.h | 3 ++ contrib/postgres_fdw/sql/postgres_fdw.sql | 32 +++++++++++- doc/src/sgml/postgres-fdw.sgml | 46 ++++++++++++++++- 6 files changed, 154 insertions(+), 5 deletions(-) diff --git a/contrib/postgres_fdw/connection.c b/contrib/postgres_fdw/connection.c index b9f6050f4b..323242c1d6 100644 --- a/contrib/postgres_fdw/connection.c +++ b/contrib/postgres_fdw/connection.c @@ -816,6 +816,7 @@ pgfdw_xact_callback(XactEvent event, void *arg) while ((entry = (ConnCacheEntry *) hash_seq_search(&scan))) { PGresult *res; + bool used_in_current_xact = false; /* Ignore cache entry if no open connection right now */ if (entry->conn == NULL) @@ -826,6 +827,8 @@ pgfdw_xact_callback(XactEvent event, void *arg) { bool abort_cleanup_failure = false; + used_in_current_xact = true; + elog(DEBUG3, "closing remote transaction on connection %p", entry->conn); @@ -960,16 +963,19 @@ pgfdw_xact_callback(XactEvent event, void *arg) /* * If the connection isn't in a good idle state or it is marked as - * invalid, then discard it to recover. Next GetConnection will open a - * new connection. + * invalid or keep_connections GUC is false and this connection is used + * in current xact, then discard it to recover. Next GetConnection will + * open a new connection. */ if (PQstatus(entry->conn) != CONNECTION_OK || PQtransactionStatus(entry->conn) != PQTRANS_IDLE || entry->changing_xact_state || - entry->invalidated) + entry->invalidated || + (used_in_current_xact && !keep_connections)) { elog(DEBUG3, "discarding connection %p", entry->conn); disconnect_pg_server(entry); + used_in_current_xact = false; } } diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out index ba29bc6131..e08d9f38be 100644 --- a/contrib/postgres_fdw/expected/postgres_fdw.out +++ b/contrib/postgres_fdw/expected/postgres_fdw.out @@ -9448,5 +9448,55 @@ DETAIL: Such connections are discarded at the end of remote transaction. (0 rows) COMMIT; +-- =================================================================== +-- Test postgres_fdw.keep_connections GUC +-- =================================================================== +-- By default, keep_connections GUC is on i.e. local session caches all the +-- foreign server connections. +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; +-- Make connection using loopback server, connection should not be cached as +-- the GUC is off. +SELECT 1 FROM ft1 LIMIT 1; + ?column? +---------- + 1 +(1 row) + +-- Should output nothing. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; + fdw_unnest +------------ +(0 rows) + +-- Set it on i.e. connections are cached. +SET postgres_fdw.keep_connections TO on; +SELECT 1 FROM ft1 LIMIT 1; + ?column? +---------- + 1 +(1 row) + +-- Should output loopback. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; + fdw_unnest +------------------ + (loopback, true) +(1 row) + +-- Discard loopback connection. +SELECT * FROM postgres_fdw_disconnect(); /* TRUE */ + postgres_fdw_disconnect +------------------------- + t +(1 row) + -- Clean up. DROP FUNCTION fdw_unnest; diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c index b6c72e1d1e..160f17972b 100644 --- a/contrib/postgres_fdw/postgres_fdw.c +++ b/contrib/postgres_fdw/postgres_fdw.c @@ -302,6 +302,8 @@ typedef struct List *already_used; /* expressions already dealt with */ } ec_member_foreign_arg; +bool keep_connections = true; + /* * SQL functions */ @@ -506,6 +508,20 @@ static void merge_fdw_options(PgFdwRelationInfo *fpinfo, const PgFdwRelationInfo *fpinfo_o, const PgFdwRelationInfo *fpinfo_i); +void +_PG_init(void) +{ + DefineCustomBoolVariable("postgres_fdw.keep_connections", + "Enables postgres_fdw connection caching.", + "When off postgres_fdw will close connections at the end of transaction.", + &keep_connections, + true, + PGC_USERSET, + 0, + NULL, + NULL, + NULL); +} /* * Foreign-data wrapper handler function: return a struct with pointers diff --git a/contrib/postgres_fdw/postgres_fdw.h b/contrib/postgres_fdw/postgres_fdw.h index eef410db39..7f1bdb96d6 100644 --- a/contrib/postgres_fdw/postgres_fdw.h +++ b/contrib/postgres_fdw/postgres_fdw.h @@ -124,9 +124,12 @@ typedef struct PgFdwRelationInfo int relation_index; } PgFdwRelationInfo; +extern bool keep_connections; + /* in postgres_fdw.c */ extern int set_transmission_modes(void); extern void reset_transmission_modes(int nestlevel); +extern void _PG_init(void); /* in connection.c */ extern PGconn *GetConnection(UserMapping *user, bool will_prep_stmt); diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql index 2267aee630..b37aa569d6 100644 --- a/contrib/postgres_fdw/sql/postgres_fdw.sql +++ b/contrib/postgres_fdw/sql/postgres_fdw.sql @@ -2875,5 +2875,35 @@ DROP SERVER temploopback2 CASCADE; SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; /* WARNING */ COMMIT; +-- =================================================================== +-- Test postgres_fdw.keep_connections GUC +-- =================================================================== + +-- By default, keep_connections GUC is on i.e. local session caches all the +-- foreign server connections. +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; + +-- Make connection using loopback server, connection should not be cached as +-- the GUC is off. +SELECT 1 FROM ft1 LIMIT 1; + +-- Should output nothing. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; + +-- Set it on i.e. connections are cached. +SET postgres_fdw.keep_connections TO on; + +SELECT 1 FROM ft1 LIMIT 1; + +-- Should output loopback. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; + +-- Discard loopback connection. +SELECT * FROM postgres_fdw_disconnect(); /* TRUE */ + -- Clean up. -DROP FUNCTION fdw_unnest; +DROP FUNCTION fdw_unnest; \ No newline at end of file diff --git a/doc/src/sgml/postgres-fdw.sgml b/doc/src/sgml/postgres-fdw.sgml index 405923f2aa..15def846f5 100644 --- a/doc/src/sgml/postgres-fdw.sgml +++ b/doc/src/sgml/postgres-fdw.sgml @@ -519,6 +519,44 @@ OPTIONS (ADD password_required 'false'); + + 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 setting postgres_fdw.keep_connections to + off does not discard any previously made and still open + connections immediately. They will be closed only at the end of future + transactions, which operated on them. To close all connections + immediately use postgres_fdw_disconnect function. + + + + + + + + + Connection Management @@ -537,12 +575,18 @@ OPTIONS (ADD password_required 'false'); 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 way to remove the connections to the remote servers and + provides following ways to remove the connections to the remote servers and so the remote sessions: postgres_fdw_disconnect() to discard all the connections or postgres_fdw_disconnect(text) to discard the connection associated with the given foreign server. + + A configuration parameter, 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. -- 2.25.1