Ensure that a cursor is scanned under the same scanCommandId it was

originally created with, so that the set of visible tuples does not
change as a result of other activity.  This essentially makes PG cursors
INSENSITIVE per the SQL92 definition.  See bug report of 13-Feb-02.

src/backend/commands/command.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/commands/Attic/command.c,v 1.152 2002/01/03 23:19:30 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/commands/Attic/command.c,v 1.153 2002/02/14 15:24:06 tgl Exp $
  *
  * NOTES
  *	  The PerformAddAttribute() code, like most of the relation
@@ -103,6 +103,7 @@ PerformPortalFetch(char *name,
 	QueryDesc  *queryDesc;
 	EState	   *estate;
 	MemoryContext oldcontext;
+	CommandId	savedId;
 	bool		temp_desc = false;
 
 	/*
@@ -156,7 +157,7 @@ PerformPortalFetch(char *name,
 	}
 
 	/*
-	 * tell the destination to prepare to receive some tuples.
+	 * Tell the destination to prepare to receive some tuples.
 	 */
 	BeginCommand(name,
 				 queryDesc->operation,
@@ -168,6 +169,14 @@ PerformPortalFetch(char *name,
 				 tag,
 				 queryDesc->dest);
 
+	/*
+	 * Restore the scanCommandId that was current when the cursor was
+	 * opened.  This ensures that we see the same tuples throughout the
+	 * execution of the cursor.
+	 */
+	savedId = GetScanCommandId();
+	SetScanCommandId(PortalGetCommandId(portal));
+
 	/*
 	 * Determine which direction to go in, and check to see if we're
 	 * already at the end of the available tuples in that direction.  If
@@ -214,6 +223,11 @@ PerformPortalFetch(char *name,
 		}
 	}
 
+	/*
+	 * Restore outer command ID.
+	 */
+	SetScanCommandId(savedId);
+
 	/*
 	 * Clean up and switch back to old context.
 	 */