Avoid multiple foreign server connections when all use same user mapping.

Previously, postgres_fdw's connection cache was keyed by user OID and
server OID, but this can lead to multiple connections when it's not
really necessary.  In particular, if all relevant users are mapped to
the public user mapping, then their connection options are certainly
the same, so one connection can be used for all of them.

While we're cleaning things up here, drop the "server" argument to
GetConnection(), which isn't really needed.  This saves a few cycles
because callers no longer have to look this up; the function itself
does, but only when establishing a new connection, not when reusing
an existing one.

Ashutosh Bapat, with a few small changes by me.

1 files changed, 10 insertions, 18 deletions

diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index 374faf5a25a..a237e152c02 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -1101,7 +1101,6 @@ postgresBeginForeignScan(ForeignScanState *node, int eflags)
 	RangeTblEntry *rte;
 	Oid			userid;
 	ForeignTable *table;
-	ForeignServer *server;
 	UserMapping *user;
 	int			numParams;
 	int			i;
@@ -1129,14 +1128,13 @@ postgresBeginForeignScan(ForeignScanState *node, int eflags)
 	/* Get info about foreign table. */
 	fsstate->rel = node->ss.ss_currentRelation;
 	table = GetForeignTable(RelationGetRelid(fsstate->rel));
-	server = GetForeignServer(table->serverid);
-	user = GetUserMapping(userid, server->serverid);
+	user = GetUserMapping(userid, table->serverid);
 
 	/*
 	 * Get connection to the foreign server.  Connection manager will
 	 * establish new connection if necessary.
 	 */
-	fsstate->conn = GetConnection(server, user, false);
+	fsstate->conn = GetConnection(user, false);
 
 	/* Assign a unique ID for my cursor */
 	fsstate->cursor_number = GetCursorNumber(fsstate->conn);
@@ -1503,7 +1501,6 @@ postgresBeginForeignModify(ModifyTableState *mtstate,
 	RangeTblEntry *rte;
 	Oid			userid;
 	ForeignTable *table;
-	ForeignServer *server;
 	UserMapping *user;
 	AttrNumber	n_params;
 	Oid			typefnoid;
@@ -1530,11 +1527,10 @@ postgresBeginForeignModify(ModifyTableState *mtstate,
 
 	/* Get info about foreign table. */
 	table = GetForeignTable(RelationGetRelid(rel));
-	server = GetForeignServer(table->serverid);
-	user = GetUserMapping(userid, server->serverid);
+	user = GetUserMapping(userid, table->serverid);
 
 	/* Open connection; report that we'll create a prepared statement. */
-	fmstate->conn = GetConnection(server, user, true);
+	fmstate->conn = GetConnection(user, true);
 	fmstate->p_name = NULL;		/* prepared statement not made yet */
 
 	/* Deconstruct fdw_private data. */
@@ -1988,7 +1984,7 @@ estimate_path_cost_size(PlannerInfo *root,
 			appendOrderByClause(&sql, root, baserel, pathkeys);
 
 		/* Get the remote estimate */
-		conn = GetConnection(fpinfo->server, fpinfo->user, false);
+		conn = GetConnection(fpinfo->user, false);
 		get_remote_estimate(sql.data, conn, &rows, &width,
 							&startup_cost, &total_cost);
 		ReleaseConnection(conn);
@@ -2544,7 +2540,6 @@ postgresAnalyzeForeignTable(Relation relation,
 							BlockNumber *totalpages)
 {
 	ForeignTable *table;
-	ForeignServer *server;
 	UserMapping *user;
 	PGconn	   *conn;
 	StringInfoData sql;
@@ -2565,9 +2560,8 @@ postgresAnalyzeForeignTable(Relation relation,
 	 * owner, even if the ANALYZE was started by some other user.
 	 */
 	table = GetForeignTable(RelationGetRelid(relation));
-	server = GetForeignServer(table->serverid);
-	user = GetUserMapping(relation->rd_rel->relowner, server->serverid);
-	conn = GetConnection(server, user, false);
+	user = GetUserMapping(relation->rd_rel->relowner, table->serverid);
+	conn = GetConnection(user, false);
 
 	/*
 	 * Construct command to get page count for relation.
@@ -2626,7 +2620,6 @@ postgresAcquireSampleRowsFunc(Relation relation, int elevel,
 {
 	PgFdwAnalyzeState astate;
 	ForeignTable *table;
-	ForeignServer *server;
 	UserMapping *user;
 	PGconn	   *conn;
 	unsigned int cursor_number;
@@ -2657,9 +2650,8 @@ postgresAcquireSampleRowsFunc(Relation relation, int elevel,
 	 * owner, even if the ANALYZE was started by some other user.
 	 */
 	table = GetForeignTable(RelationGetRelid(relation));
-	server = GetForeignServer(table->serverid);
-	user = GetUserMapping(relation->rd_rel->relowner, server->serverid);
-	conn = GetConnection(server, user, false);
+	user = GetUserMapping(relation->rd_rel->relowner, table->serverid);
+	conn = GetConnection(user, false);
 
 	/*
 	 * Construct cursor that retrieves whole rows from remote.
@@ -2860,7 +2852,7 @@ postgresImportForeignSchema(ImportForeignSchemaStmt *stmt, Oid serverOid)
 	 */
 	server = GetForeignServer(serverOid);
 	mapping = GetUserMapping(GetUserId(), server->serverid);
-	conn = GetConnection(server, mapping, false);
+	conn = GetConnection(mapping, false);
 
 	/* Don't attempt to import collation if remote server hasn't got it */
 	if (PQserverVersion(conn) < 90100)