Modify UPDATE/DELETE WHERE CURRENT OF to use the FOR UPDATE infrastructure to

locate the target row, if the cursor was declared with FOR UPDATE or FOR
SHARE.  This approach is more flexible and reliable than digging through the
plan tree; for instance it can cope with join cursors.  But we still provide
the old code for use with non-FOR-UPDATE cursors.  Per gripe from Robert Haas.

1 files changed, 110 insertions, 42 deletions

diff --git a/src/backend/executor/execCurrent.c b/src/backend/executor/execCurrent.c
index 5ae90c68f40..2f2270cfab3 100644
--- a/src/backend/executor/execCurrent.c
+++ b/src/backend/executor/execCurrent.c
@@ -6,7 +6,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- *	$PostgreSQL: pgsql/src/backend/executor/execCurrent.c,v 1.7 2008/05/12 00:00:48 alvherre Exp $
+ *	$PostgreSQL: pgsql/src/backend/executor/execCurrent.c,v 1.8 2008/11/16 17:34:28 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -46,10 +46,6 @@ execCurrentOf(CurrentOfExpr *cexpr,
 	char	   *table_name;
 	Portal		portal;
 	QueryDesc  *queryDesc;
-	ScanState  *scanstate;
-	bool		lisnull;
-	Oid			tuple_tableoid;
-	ItemPointer tuple_tid;
 
 	/* Get the cursor name --- may have to look up a parameter reference */
 	if (cexpr->cursor_name)
@@ -79,57 +75,129 @@ execCurrentOf(CurrentOfExpr *cexpr,
 				 errmsg("cursor \"%s\" is not a SELECT query",
 						cursor_name)));
 	queryDesc = PortalGetQueryDesc(portal);
-	if (queryDesc == NULL)
+	if (queryDesc == NULL || queryDesc->estate == NULL)
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_CURSOR_STATE),
 				 errmsg("cursor \"%s\" is held from a previous transaction",
 						cursor_name)));
 
 	/*
-	 * Dig through the cursor's plan to find the scan node.  Fail if it's not
-	 * there or buried underneath aggregation.
+	 * We have two different strategies depending on whether the cursor uses
+	 * FOR UPDATE/SHARE or not.  The reason for supporting both is that the
+	 * FOR UPDATE code is able to identify a target table in many cases where
+	 * the other code can't, while the non-FOR-UPDATE case allows use of WHERE
+	 * CURRENT OF with an insensitive cursor.
 	 */
-	scanstate = search_plan_tree(ExecGetActivePlanTree(queryDesc),
-								 table_oid);
-	if (!scanstate)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_CURSOR_STATE),
-		errmsg("cursor \"%s\" is not a simply updatable scan of table \"%s\"",
-			   cursor_name, table_name)));
+	if (queryDesc->estate->es_rowMarks)
+	{
+		ExecRowMark *erm;
+		ListCell   *lc;
 
-	/*
-	 * The cursor must have a current result row: per the SQL spec, it's an
-	 * error if not.  We test this at the top level, rather than at the scan
-	 * node level, because in inheritance cases any one table scan could
-	 * easily not be on a row.	We want to return false, not raise error, if
-	 * the passed-in table OID is for one of the inactive scans.
-	 */
-	if (portal->atStart || portal->atEnd)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_CURSOR_STATE),
-				 errmsg("cursor \"%s\" is not positioned on a row",
-						cursor_name)));
+		/*
+		 * Here, the query must have exactly one FOR UPDATE/SHARE reference to
+		 * the target table, and we dig the ctid info out of that.
+		 */
+		erm = NULL;
+		foreach(lc, queryDesc->estate->es_rowMarks)
+		{
+			ExecRowMark *thiserm = (ExecRowMark *) lfirst(lc);
+
+			if (RelationGetRelid(thiserm->relation) == table_oid)
+			{
+				if (erm)
+					ereport(ERROR,
+							(errcode(ERRCODE_INVALID_CURSOR_STATE),
+							 errmsg("cursor \"%s\" has multiple FOR UPDATE/SHARE references to table \"%s\"",
+									cursor_name, table_name)));
+				erm = thiserm;
+			}
+		}
 
-	/* Now OK to return false if we found an inactive scan */
-	if (TupIsNull(scanstate->ss_ScanTupleSlot))
+		if (erm == NULL)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_CURSOR_STATE),
+					 errmsg("cursor \"%s\" does not have a FOR UPDATE/SHARE reference to table \"%s\"",
+							cursor_name, table_name)));
+
+		/*
+		 * The cursor must have a current result row: per the SQL spec, it's
+		 * an error if not.
+		 */
+		if (portal->atStart || portal->atEnd)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_CURSOR_STATE),
+					 errmsg("cursor \"%s\" is not positioned on a row",
+							cursor_name)));
+
+		/* Return the currently scanned TID, if there is one */
+		if (ItemPointerIsValid(&(erm->curCtid)))
+		{
+			*current_tid = erm->curCtid;
+			return true;
+		}
+
+		/*
+		 * This table didn't produce the cursor's current row; some other
+		 * inheritance child of the same parent must have.  Signal caller
+		 * to do nothing on this table.
+		 */
 		return false;
+	}
+	else
+	{
+		ScanState  *scanstate;
+		bool		lisnull;
+		Oid			tuple_tableoid;
+		ItemPointer tuple_tid;
+
+		/*
+		 * Without FOR UPDATE, we dig through the cursor's plan to find the
+		 * scan node.  Fail if it's not there or buried underneath
+		 * aggregation.
+		 */
+		scanstate = search_plan_tree(ExecGetActivePlanTree(queryDesc),
+									 table_oid);
+		if (!scanstate)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_CURSOR_STATE),
+					 errmsg("cursor \"%s\" is not a simply updatable scan of table \"%s\"",
+							cursor_name, table_name)));
 
-	/* Use slot_getattr to catch any possible mistakes */
-	tuple_tableoid = DatumGetObjectId(slot_getattr(scanstate->ss_ScanTupleSlot,
-												   TableOidAttributeNumber,
-												   &lisnull));
-	Assert(!lisnull);
-	tuple_tid = (ItemPointer)
-		DatumGetPointer(slot_getattr(scanstate->ss_ScanTupleSlot,
-									 SelfItemPointerAttributeNumber,
-									 &lisnull));
-	Assert(!lisnull);
+		/*
+		 * The cursor must have a current result row: per the SQL spec, it's
+		 * an error if not.  We test this at the top level, rather than at the
+		 * scan node level, because in inheritance cases any one table scan
+		 * could easily not be on a row. We want to return false, not raise
+		 * error, if the passed-in table OID is for one of the inactive scans.
+		 */
+		if (portal->atStart || portal->atEnd)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_CURSOR_STATE),
+					 errmsg("cursor \"%s\" is not positioned on a row",
+							cursor_name)));
 
-	Assert(tuple_tableoid == table_oid);
+		/* Now OK to return false if we found an inactive scan */
+		if (TupIsNull(scanstate->ss_ScanTupleSlot))
+			return false;
 
-	*current_tid = *tuple_tid;
+		/* Use slot_getattr to catch any possible mistakes */
+		tuple_tableoid =
+			DatumGetObjectId(slot_getattr(scanstate->ss_ScanTupleSlot,
+										  TableOidAttributeNumber,
+										  &lisnull));
+		Assert(!lisnull);
+		tuple_tid = (ItemPointer)
+			DatumGetPointer(slot_getattr(scanstate->ss_ScanTupleSlot,
+										 SelfItemPointerAttributeNumber,
+										 &lisnull));
+		Assert(!lisnull);
 
-	return true;
+		Assert(tuple_tableoid == table_oid);
+
+		*current_tid = *tuple_tid;
+
+		return true;
+	}
 }
 
 /*