Move the handling of SELECT FOR UPDATE locking and rechecking out of

execMain.c and into a new plan node type LockRows.  Like the recent change
to put table updating into a ModifyTable plan node, this increases planning
flexibility by allowing the operations to occur below the top level of the
plan tree.  It's necessary in any case to restore the previous behavior of
having FOR UPDATE locking occur before ModifyTable does.

This partially refactors EvalPlanQual to allow multiple rows-under-test
to be inserted into the EPQ machinery before starting an EPQ test query.
That isn't sufficient to fix EPQ's general bogosity in the face of plans
that return multiple rows per test row, though.  Since this patch is
mostly about getting some plan node infrastructure in place and not about
fixing ten-year-old bugs, I will leave EPQ improvements for another day.

Another behavioral change that we could now think about is doing FOR UPDATE
before LIMIT, but that too seems like it should be treated as a followon
patch.

src/include/nodes/execnodes.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/nodes/execnodes.h,v 1.209 2009/10/10 01:43:50 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/nodes/execnodes.h,v 1.210 2009/10/12 18:10:51 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -332,6 +332,8 @@ typedef struct EState
 	Snapshot	es_crosscheck_snapshot; /* crosscheck time qual for RI */
 	List	   *es_range_table; /* List of RangeTblEntry */
 
+	JunkFilter *es_junkFilter;	/* top-level junk filter, if any */
+
 	/* If query can insert/delete tuples, the command ID to mark them with */
 	CommandId	es_output_cid;
 
@@ -339,7 +341,6 @@ typedef struct EState
 	ResultRelInfo *es_result_relations; /* array of ResultRelInfos */
 	int			es_num_result_relations;		/* length of array */
 	ResultRelInfo *es_result_relation_info;		/* currently active array elt */
-	JunkFilter *es_junkFilter;	/* top-level junk filter, if any */
 
 	/* Stuff used for firing triggers: */
 	List	   *es_trig_target_relations;		/* trigger-only ResultRelInfos */
@@ -354,9 +355,10 @@ typedef struct EState
 
 	List	   *es_tupleTable;	/* List of TupleTableSlots */
 
+	List	   *es_rowMarks;	/* List of ExecRowMarks */
+
 	uint32		es_processed;	/* # of tuples processed */
 	Oid			es_lastoid;		/* last oid processed (by INSERT) */
-	List	   *es_rowMarks;	/* not good place, but there is no other */
 
 	bool		es_instrument;	/* true requests runtime instrumentation */
 	bool		es_select_into; /* true if doing SELECT INTO */
@@ -378,19 +380,22 @@ typedef struct EState
 	struct evalPlanQual *es_evalPlanQual;		/* chain of PlanQual states */
 	bool	   *es_evTupleNull; /* local array of EPQ status */
 	HeapTuple  *es_evTuple;		/* shared array of EPQ substitute tuples */
-	bool		es_useEvalPlan; /* evaluating EPQ tuples? */
 } EState;
 
 
 /*
- * es_rowMarks is a list of these structs.	See RowMarkClause for details
- * about rti and prti.	toidAttno is not used in a "plain" rowmark.
+ * es_rowMarks is a list of these structs.  Each LockRows node has its own
+ * list, which is the subset of locks that it is supposed to enforce; note
+ * that the per-node lists point to the same structs that are in the global
+ * list.  See RowMarkClause for details about rti, prti, and rowmarkId.
+ * toidAttno is not used in a "plain" (non-inherited) rowmark.
  */
 typedef struct ExecRowMark
 {
 	Relation	relation;		/* opened and RowShareLock'd relation */
 	Index		rti;			/* its range table index */
 	Index		prti;			/* parent range table index, if child */
+	Index		rowmarkId;		/* unique identifier assigned by planner */
 	bool		forUpdate;		/* true = FOR UPDATE, false = FOR SHARE */
 	bool		noWait;			/* NOWAIT option */
 	AttrNumber	ctidAttNo;		/* resno of its ctid junk attribute */
@@ -1636,6 +1641,20 @@ typedef struct SetOpState
 	TupleHashIterator hashiter; /* for iterating through hash table */
 } SetOpState;
 
+/* ----------------
+ *	 LockRowsState information
+ *
+ *		LockRows nodes are used to enforce FOR UPDATE/FOR SHARE locking.
+ * ----------------
+ */
+typedef struct LockRowsState
+{
+	PlanState	ps;				/* its first field is NodeTag */
+	List	   *lr_rowMarks;	/* List of ExecRowMarks */
+	JunkFilter *lr_junkFilter;	/* needed for getting ctid columns */
+	bool		lr_useEvalPlan;	/* evaluating EPQ tuples? */
+} LockRowsState;
+
 /* ----------------
  *	 LimitState information
  *