Revise nodeMergejoin in light of example provided by Guillaume Smet.

When one side of the join has a NULL, we don't want to uselessly try
to match it against every remaining tuple of the other side.  While
at it, rewrite the comparison machinery to avoid multiple evaluations
of the left and right input expressions and to use a btree comparator
where available, instead of double operator calls.  Also revise the
state machine to eliminate redundant comparisons and hopefully make it
more readable too.

1 files changed, 16 insertions, 10 deletions

diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 2d74d25a361..9d47c17ad23 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/nodes/execnodes.h,v 1.131 2005/05/05 03:37:23 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/nodes/execnodes.h,v 1.132 2005/05/13 21:20:16 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1028,24 +1028,28 @@ typedef struct NestLoopState
 /* ----------------
  *	 MergeJoinState information
  *
- *		OuterSkipQual	   outerKey1 < innerKey1 ...
- *		InnerSkipQual	   outerKey1 > innerKey1 ...
- *		JoinState		   current "state" of join. see executor.h
+ *		NumClauses		   number of mergejoinable join clauses
+ *		Clauses			   info for each mergejoinable clause
+ *		JoinState		   current "state" of join.  see execdefs.h
  *		MatchedOuter	   true if found a join match for current outer tuple
  *		MatchedInner	   true if found a join match for current inner tuple
- *		OuterTupleSlot	   pointer to slot in tuple table for cur outer tuple
- *		InnerTupleSlot	   pointer to slot in tuple table for cur inner tuple
- *		MarkedTupleSlot    pointer to slot in tuple table for marked tuple
+ *		OuterTupleSlot	   slot in tuple table for cur outer tuple
+ *		InnerTupleSlot	   slot in tuple table for cur inner tuple
+ *		MarkedTupleSlot    slot in tuple table for marked tuple
  *		NullOuterTupleSlot prepared null tuple for right outer joins
  *		NullInnerTupleSlot prepared null tuple for left outer joins
+ *		OuterEContext	   workspace for computing outer tuple's join values
+ *		InnerEContext	   workspace for computing inner tuple's join values
  * ----------------
  */
+/* private in nodeMergejoin.c: */
+typedef struct MergeJoinClauseData *MergeJoinClause;
+
 typedef struct MergeJoinState
 {
 	JoinState	js;				/* its first field is NodeTag */
-	List	   *mergeclauses;	/* list of ExprState nodes */
-	List	   *mj_OuterSkipQual;		/* list of ExprState nodes */
-	List	   *mj_InnerSkipQual;		/* list of ExprState nodes */
+	int			mj_NumClauses;
+	MergeJoinClause mj_Clauses;	/* array of length mj_NumClauses */
 	int			mj_JoinState;
 	bool		mj_MatchedOuter;
 	bool		mj_MatchedInner;
@@ -1054,6 +1058,8 @@ typedef struct MergeJoinState
 	TupleTableSlot *mj_MarkedTupleSlot;
 	TupleTableSlot *mj_NullOuterTupleSlot;
 	TupleTableSlot *mj_NullInnerTupleSlot;
+	ExprContext *mj_OuterEContext;
+	ExprContext *mj_InnerEContext;
 } MergeJoinState;
 
 /* ----------------