Re-implement EvalPlanQual processing to improve its performance and eliminate

a lot of strange behaviors that occurred in join cases.  We now identify the
"current" row for every joined relation in UPDATE, DELETE, and SELECT FOR
UPDATE/SHARE queries.  If an EvalPlanQual recheck is necessary, we jam the
appropriate row into each scan node in the rechecking plan, forcing it to emit
only that one row.  The former behavior could rescan the whole of each joined
relation for each recheck, which was terrible for performance, and what's much
worse could result in duplicated output tuples.

Also, the original implementation of EvalPlanQual could not re-use the recheck
execution tree --- it had to go through a full executor init and shutdown for
every row to be tested.  To avoid this overhead, I've associated a special
runtime Param with each LockRows or ModifyTable plan node, and arranged to
make every scan node below such a node depend on that Param.  Thus, by
signaling a change in that Param, the EPQ machinery can just rescan the
already-built test plan.

This patch also adds a prohibition on set-returning functions in the
targetlist of SELECT FOR UPDATE/SHARE.  This is needed to avoid the
duplicate-output-tuple problem.  It seems fairly reasonable since the
other restrictions on SELECT FOR UPDATE are meant to ensure that there
is a unique correspondence between source tuples and result tuples,
which an output SRF destroys as much as anything else does.

src/include/nodes/parsenodes.h

@@ -13,7 +13,7 @@
  * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/nodes/parsenodes.h,v 1.410 2009/10/14 22:14:24 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/nodes/parsenodes.h,v 1.411 2009/10/26 02:26:41 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -800,28 +800,17 @@ typedef struct WindowClause
 
 /*
  * RowMarkClause -
- *	   representation of FOR UPDATE/SHARE clauses
+ *	   parser output representation of FOR UPDATE/SHARE clauses
  *
- * We create a separate RowMarkClause node for each target relation.  In the
- * output of the parser and rewriter, all RowMarkClauses have rti == prti and
- * isParent == false.  When the planner discovers that a target relation
- * is the root of an inheritance tree, it sets isParent true, and adds an
- * additional RowMarkClause to the list for each child relation (including
- * the target rel itself in its role as a child).  The child entries have
- * rti == child rel's RT index, prti == parent's RT index, and can therefore
- * be recognized as children by the fact that prti != rti.
- * rowmarkId is a unique ID for the RowMarkClause across an entire query,
- * and is assigned during planning; it's always zero upstream of the planner.
+ * Query.rowMarks contains a separate RowMarkClause node for each relation
+ * identified as a FOR UPDATE/SHARE target.
  */
 typedef struct RowMarkClause
 {
 	NodeTag		type;
 	Index		rti;			/* range table index of target relation */
-	Index		prti;			/* range table index of parent relation */
-	Index		rowmarkId;		/* unique identifier assigned by planner */
 	bool		forUpdate;		/* true = FOR UPDATE, false = FOR SHARE */
 	bool		noWait;			/* NOWAIT option */
-	bool		isParent;		/* set by planner when expanding inheritance */
 } RowMarkClause;
 
 /*