From: Shigeru Hanada <hanada@metrosystems.co.jp>
Date: Tue, 9 Nov 2010 06:07:36 +0000 (+0900)
Subject: Add new FdwRoutine function BeginScan which is called just after Open
X-Git-Url: http://git.postgresql.org/gitweb/static/gitweb.js?a=commitdiff_plain;h=84e508d574dc9faef48bc71b8d7bf85d33870209;p=users%2Fhanada%2Fpostgres.git

Add new FdwRoutine function BeginScan which is called just after Open
if the execution if for real query or EXPLAIN ANALYZE.
---

diff --git a/contrib/postgresql_fdw/postgresql_fdw.c b/contrib/postgresql_fdw/postgresql_fdw.c
index 288830430b..f327a298f1 100644
--- a/contrib/postgresql_fdw/postgresql_fdw.c
+++ b/contrib/postgresql_fdw/postgresql_fdw.c
@@ -43,6 +43,7 @@ extern Datum postgresql_fdw_handler(PG_FUNCTION_ARGS);
 static FSConnection* pgConnectServer(ForeignServer *server, UserMapping *user);
 static void pgFreeFSConnection(FSConnection *conn);
 static void pgOpen(ForeignScanState *scanstate);
+static void pgBeginScan(ForeignScanState *scanstate);
 static void pgIterate(ForeignScanState *scanstate);
 static void pgClose(ForeignScanState *scanstate);
 static void pgReOpen(ForeignScanState *scanstate);
@@ -74,6 +75,7 @@ static FdwRoutine postgresql_fdw_routine =
 	pgFreeFSConnection,
 	pgEstimateCosts,
 	pgOpen,
+	pgBeginScan,
 	pgIterate,
 	pgClose,
 	pgReOpen,
@@ -491,6 +493,16 @@ pgOpen(ForeignScanState *scanstate)
 	scanstate->reply = (FdwReply *) reply;
 }
 
+/*
+ * Initiate actual scan on a foreign table.
+ * This function is called just after pgOpen() if the exexution was for real
+ * query or EXPLAIN ANALYZE.
+ */
+static void
+pgBeginScan(ForeignScanState *scanstate)
+{
+}
+
 /*
  * return tuples one by one.
  *   - execute SQL statement which was deparsed in pgOpen()
diff --git a/src/backend/executor/nodeForeignscan.c b/src/backend/executor/nodeForeignscan.c
index f8c305a6ae..c9634c6b46 100644
--- a/src/backend/executor/nodeForeignscan.c
+++ b/src/backend/executor/nodeForeignscan.c
@@ -170,12 +170,20 @@ ExecInitForeignScan(ForeignScan *node, EState *estate, int eflags)
 	scanstate->wrapper = GetForeignDataWrapper(scanstate->server->fdwid);
 	scanstate->user = GetUserMapping(userid, scanstate->server->serverid);
 	scanstate->routine = GetFdwRoutine(scanstate->wrapper->fdwhandler);
-
-	/* connect to the foreign server and prepare to execute scan */
-	scanstate->conn = scanstate->routine->ConnectServer(scanstate->server,
-														scanstate->user);
 	scanstate->routine->Open(scanstate);
 
+	/*
+	 * If this execution was not for EXPLAIN w/o ANALYZE flag, initiate the
+	 * foreign scan.
+	 */
+	if (!(eflags & EXEC_FLAG_EXPLAIN_ONLY))
+	{
+		/* connect to the foreign server and prepare to execute scan */
+		scanstate->conn = scanstate->routine->ConnectServer(scanstate->server,
+															scanstate->user);
+		scanstate->routine->BeginScan(scanstate);
+	}
+
 	return scanstate;
 }
 
diff --git a/src/backend/foreign/file_fdw.c b/src/backend/foreign/file_fdw.c
index 729f4692d0..707a3eeedc 100644
--- a/src/backend/foreign/file_fdw.c
+++ b/src/backend/foreign/file_fdw.c
@@ -70,6 +70,7 @@ extern Datum file_fdw_handler(PG_FUNCTION_ARGS);
 static FSConnection* ConnectServer(ForeignServer *server, UserMapping *user);
 static void FreeFSConnection(FSConnection *conn);
 static void Open(ForeignScanState *scanstate);
+static void BeginScan(ForeignScanState *scanstate);
 static void Iterate(ForeignScanState *scanstate);
 static void Close(ForeignScanState *scanstate);
 static void ReOpen(ForeignScanState *scanstate);
@@ -253,6 +254,7 @@ file_fdw_handler(PG_FUNCTION_ARGS)
 		FreeFSConnection,
 		EstimateCosts,
 		Open,
+		BeginScan,
 		Iterate,
 		Close,
 		ReOpen,
@@ -302,6 +304,16 @@ Open(ForeignScanState *scanstate)
 	scanstate->reply = (FdwReply *) fstate;
 }
 
+/*
+ * BeginScan()
+ *   - initiate access to the file, but we have nothing to do
+ */
+static void
+BeginScan(ForeignScanState *scanstate)
+{
+	elog(DEBUG2, "%s called", __FUNCTION__);
+}
+
 /*
  * Iterate()
  *   - create HeapTuple from the record in the file.
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 70cfb1084b..2abda678bc 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -1430,10 +1430,15 @@ struct FdwRoutine
 						  RelOptInfo *baserel);
 
 	/*
-	 * Deparse query request and open a cursor for the foreign scan.
+	 * Prepare to execute foreign access.
 	 */
 	void (*Open)(ForeignScanState *scanstate);
 
+	/*
+	 * Initiate scanning of a foreign table.
+	 */
+	void (*BeginScan)(ForeignScanState *scanstate);
+
 	/*
 	 * Fetch the next record and fill tupleslot with it.
 	 */