diff --git a/src/backend/executor/nodeMergejoin.c b/src/backend/executor/nodeMergejoin.c
index cc15e5ab48..bde0f3d874 100644
--- a/src/backend/executor/nodeMergejoin.c
+++ b/src/backend/executor/nodeMergejoin.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/nodeMergejoin.c,v 1.97.2.1 2010/01/05 23:25:44 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/nodeMergejoin.c,v 1.97.2.2 2010/05/28 01:14:11 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -131,6 +131,14 @@ typedef struct MergeJoinClauseData
 	FmgrInfo	cmpfinfo;
 } MergeJoinClauseData;
 
+/* Result type for MJEvalOuterValues and MJEvalInnerValues */
+typedef enum
+{
+	MJEVAL_MATCHABLE,			/* normal, potentially matchable tuple */
+	MJEVAL_NONMATCHABLE,		/* tuple cannot join because it has a null */
+	MJEVAL_ENDOFJOIN			/* end of input (physical or effective) */
+} MJEvalResult;
+
 
 #define MarkInnerTuple(innerTupleSlot, mergestate) \
 	ExecCopySlot((mergestate)->mj_MarkedTupleSlot, (innerTupleSlot))
@@ -241,19 +249,34 @@ MJExamineQuals(List *mergeclauses,
  * Compute the values of the mergejoined expressions for the current
  * outer tuple.  We also detect whether it's impossible for the current
  * outer tuple to match anything --- this is true if it yields a NULL
- * input, since we assume mergejoin operators are strict.
+ * input, since we assume mergejoin operators are strict.  If the NULL
+ * is in the first join column, and that column sorts nulls last, then
+ * we can further conclude that no following tuple can match anything
+ * either, since they must all have nulls in the first column.  However,
+ * that case is only interesting if we're not in FillOuter mode, else
+ * we have to visit all the tuples anyway.
+ *
+ * For the convenience of callers, we also make this routine responsible
+ * for testing for end-of-input (null outer tuple), and returning
+ * MJEVAL_ENDOFJOIN when that's seen.  This allows the same code to be used
+ * for both real end-of-input and the effective end-of-input represented by
+ * a first-column NULL.
  *
  * We evaluate the values in OuterEContext, which can be reset each
  * time we move to a new tuple.
  */
-static bool
+static MJEvalResult
 MJEvalOuterValues(MergeJoinState *mergestate)
 {
 	ExprContext *econtext = mergestate->mj_OuterEContext;
-	bool		canmatch = true;
+	MJEvalResult result = MJEVAL_MATCHABLE;
 	int			i;
 	MemoryContext oldContext;
 
+	/* Check for end of outer subplan */
+	if (TupIsNull(mergestate->mj_OuterTupleSlot))
+		return MJEVAL_ENDOFJOIN;
+
 	ResetExprContext(econtext);
 
 	oldContext = MemoryContextSwitchTo(econtext->ecxt_per_tuple_memory);
@@ -267,12 +290,18 @@ MJEvalOuterValues(MergeJoinState *mergestate)
 		clause->ldatum = ExecEvalExpr(clause->lexpr, econtext,
 									  &clause->lisnull, NULL);
 		if (clause->lisnull)
-			canmatch = false;
+		{
+			/* match is impossible; can we end the join early? */
+			if (i == 0 && !clause->nulls_first && !mergestate->mj_FillOuter)
+				result = MJEVAL_ENDOFJOIN;
+			else if (result == MJEVAL_MATCHABLE)
+				result = MJEVAL_NONMATCHABLE;
+		}
 	}
 
 	MemoryContextSwitchTo(oldContext);
 
-	return canmatch;
+	return result;
 }
 
 /*
@@ -282,14 +311,18 @@ MJEvalOuterValues(MergeJoinState *mergestate)
  * to load data from either the true current inner, or the marked inner,
  * so caller must tell us which slot to load from.
  */
-static bool
+static MJEvalResult
 MJEvalInnerValues(MergeJoinState *mergestate, TupleTableSlot *innerslot)
 {
 	ExprContext *econtext = mergestate->mj_InnerEContext;
-	bool		canmatch = true;
+	MJEvalResult result = MJEVAL_MATCHABLE;
 	int			i;
 	MemoryContext oldContext;
 
+	/* Check for end of inner subplan */
+	if (TupIsNull(innerslot))
+		return MJEVAL_ENDOFJOIN;
+
 	ResetExprContext(econtext);
 
 	oldContext = MemoryContextSwitchTo(econtext->ecxt_per_tuple_memory);
@@ -303,12 +336,18 @@ MJEvalInnerValues(MergeJoinState *mergestate, TupleTableSlot *innerslot)
 		clause->rdatum = ExecEvalExpr(clause->rexpr, econtext,
 									  &clause->risnull, NULL);
 		if (clause->risnull)
-			canmatch = false;
+		{
+			/* match is impossible; can we end the join early? */
+			if (i == 0 && !clause->nulls_first && !mergestate->mj_FillInner)
+				result = MJEVAL_ENDOFJOIN;
+			else if (result == MJEVAL_MATCHABLE)
+				result = MJEVAL_NONMATCHABLE;
+		}
 	}
 
 	MemoryContextSwitchTo(oldContext);
 
-	return canmatch;
+	return result;
 }
 
 /*
@@ -656,46 +695,46 @@ ExecMergeJoin(MergeJoinState *node)
 
 				outerTupleSlot = ExecProcNode(outerPlan);
 				node->mj_OuterTupleSlot = outerTupleSlot;
-				if (TupIsNull(outerTupleSlot))
-				{
-					MJ_printf("ExecMergeJoin: nothing in outer subplan\n");
-					if (doFillInner)
-					{
-						/*
-						 * Need to emit right-join tuples for remaining inner
-						 * tuples.	We set MatchedInner = true to force the
-						 * ENDOUTER state to advance inner.
-						 */
-						node->mj_JoinState = EXEC_MJ_ENDOUTER;
-						node->mj_MatchedInner = true;
-						break;
-					}
-					/* Otherwise we're done. */
-					return NULL;
-				}
 
 				/* Compute join values and check for unmatchability */
-				if (MJEvalOuterValues(node))
+				switch (MJEvalOuterValues(node))
 				{
-					/* OK to go get the first inner tuple */
-					node->mj_JoinState = EXEC_MJ_INITIALIZE_INNER;
-				}
-				else
-				{
-					/* Stay in same state to fetch next outer tuple */
-					if (doFillOuter)
-					{
-						/*
-						 * Generate a fake join tuple with nulls for the inner
-						 * tuple, and return it if it passes the non-join
-						 * quals.
-						 */
-						TupleTableSlot *result;
+					case MJEVAL_MATCHABLE:
+						/* OK to go get the first inner tuple */
+						node->mj_JoinState = EXEC_MJ_INITIALIZE_INNER;
+						break;
+					case MJEVAL_NONMATCHABLE:
+						/* Stay in same state to fetch next outer tuple */
+						if (doFillOuter)
+						{
+							/*
+							 * Generate a fake join tuple with nulls for the
+							 * inner tuple, and return it if it passes the
+							 * non-join quals.
+							 */
+							TupleTableSlot *result;
 
-						result = MJFillOuter(node);
-						if (result)
-							return result;
-					}
+							result = MJFillOuter(node);
+							if (result)
+								return result;
+						}
+						break;
+					case MJEVAL_ENDOFJOIN:
+						/* No more outer tuples */
+						MJ_printf("ExecMergeJoin: nothing in outer subplan\n");
+						if (doFillInner)
+						{
+							/*
+							 * Need to emit right-join tuples for remaining
+							 * inner tuples. We set MatchedInner = true to
+							 * force the ENDOUTER state to advance inner.
+							 */
+							node->mj_JoinState = EXEC_MJ_ENDOUTER;
+							node->mj_MatchedInner = true;
+							break;
+						}
+						/* Otherwise we're done. */
+						return NULL;
 				}
 				break;
 
@@ -704,53 +743,54 @@ ExecMergeJoin(MergeJoinState *node)
 
 				innerTupleSlot = ExecProcNode(innerPlan);
 				node->mj_InnerTupleSlot = innerTupleSlot;
-				if (TupIsNull(innerTupleSlot))
-				{
-					MJ_printf("ExecMergeJoin: nothing in inner subplan\n");
-					if (doFillOuter)
-					{
-						/*
-						 * Need to emit left-join tuples for all outer tuples,
-						 * including the one we just fetched.  We set
-						 * MatchedOuter = false to force the ENDINNER state to
-						 * emit first tuple before advancing outer.
-						 */
-						node->mj_JoinState = EXEC_MJ_ENDINNER;
-						node->mj_MatchedOuter = false;
-						break;
-					}
-					/* Otherwise we're done. */
-					return NULL;
-				}
 
 				/* Compute join values and check for unmatchability */
-				if (MJEvalInnerValues(node, innerTupleSlot))
+				switch (MJEvalInnerValues(node, innerTupleSlot))
 				{
-					/*
-					 * OK, we have the initial tuples.	Begin by skipping
-					 * non-matching tuples.
-					 */
-					node->mj_JoinState = EXEC_MJ_SKIP_TEST;
-				}
-				else
-				{
-					/* Mark before advancing, if wanted */
-					if (node->mj_ExtraMarks)
-						ExecMarkPos(innerPlan);
-					/* Stay in same state to fetch next inner tuple */
-					if (doFillInner)
-					{
+					case MJEVAL_MATCHABLE:
 						/*
-						 * Generate a fake join tuple with nulls for the outer
-						 * tuple, and return it if it passes the non-join
-						 * quals.
+						 * OK, we have the initial tuples.	Begin by skipping
+						 * non-matching tuples.
 						 */
-						TupleTableSlot *result;
+						node->mj_JoinState = EXEC_MJ_SKIP_TEST;
+						break;
+					case MJEVAL_NONMATCHABLE:
+						/* Mark before advancing, if wanted */
+						if (node->mj_ExtraMarks)
+							ExecMarkPos(innerPlan);
+						/* Stay in same state to fetch next inner tuple */
+						if (doFillInner)
+						{
+							/*
+							 * Generate a fake join tuple with nulls for the
+							 * outer tuple, and return it if it passes the
+							 * non-join quals.
+							 */
+							TupleTableSlot *result;
 
-						result = MJFillInner(node);
-						if (result)
-							return result;
-					}
+							result = MJFillInner(node);
+							if (result)
+								return result;
+						}
+						break;
+					case MJEVAL_ENDOFJOIN:
+						/* No more inner tuples */
+						MJ_printf("ExecMergeJoin: nothing in inner subplan\n");
+						if (doFillOuter)
+						{
+							/*
+							 * Need to emit left-join tuples for all outer
+							 * tuples, including the one we just fetched.  We
+							 * set MatchedOuter = false to force the ENDINNER
+							 * state to emit first tuple before advancing
+							 * outer.
+							 */
+							node->mj_JoinState = EXEC_MJ_ENDINNER;
+							node->mj_MatchedOuter = false;
+							break;
+						}
+						/* Otherwise we're done. */
+						return NULL;
 				}
 				break;
 
@@ -878,41 +918,51 @@ ExecMergeJoin(MergeJoinState *node)
 				MJ_DEBUG_PROC_NODE(innerTupleSlot);
 				node->mj_MatchedInner = false;
 
-				if (TupIsNull(innerTupleSlot))
+				/* Compute join values and check for unmatchability */
+				switch (MJEvalInnerValues(node, innerTupleSlot))
 				{
-					node->mj_JoinState = EXEC_MJ_NEXTOUTER;
-					break;
-				}
+					case MJEVAL_MATCHABLE:
+						/*
+						 * Test the new inner tuple to see if it matches
+						 * outer.
+						 *
+						 * If they do match, then we join them and move on to
+						 * the next inner tuple (EXEC_MJ_JOINTUPLES).
+						 *
+						 * If they do not match then advance to next outer
+						 * tuple.
+						 */
+						compareResult = MJCompare(node);
+						MJ_DEBUG_COMPARE(compareResult);
 
-				/*
-				 * Load up the new inner tuple's comparison values.  If we see
-				 * that it contains a NULL and hence can't match any outer
-				 * tuple, we can skip the comparison and assume the new tuple
-				 * is greater than current outer.
-				 */
-				if (!MJEvalInnerValues(node, innerTupleSlot))
-				{
-					node->mj_JoinState = EXEC_MJ_NEXTOUTER;
-					break;
-				}
-
-				/*
-				 * Test the new inner tuple to see if it matches outer.
-				 *
-				 * If they do match, then we join them and move on to the next
-				 * inner tuple (EXEC_MJ_JOINTUPLES).
-				 *
-				 * If they do not match then advance to next outer tuple.
-				 */
-				compareResult = MJCompare(node);
-				MJ_DEBUG_COMPARE(compareResult);
-
-				if (compareResult == 0)
-					node->mj_JoinState = EXEC_MJ_JOINTUPLES;
-				else
-				{
-					Assert(compareResult < 0);
-					node->mj_JoinState = EXEC_MJ_NEXTOUTER;
+						if (compareResult == 0)
+							node->mj_JoinState = EXEC_MJ_JOINTUPLES;
+						else
+						{
+							Assert(compareResult < 0);
+							node->mj_JoinState = EXEC_MJ_NEXTOUTER;
+						}
+						break;
+					case MJEVAL_NONMATCHABLE:
+						/*
+						 * It contains a NULL and hence can't match any outer
+						 * tuple, so we can skip the comparison and assume the
+						 * new tuple is greater than current outer.
+						 */
+						node->mj_JoinState = EXEC_MJ_NEXTOUTER;
+						break;
+					case MJEVAL_ENDOFJOIN:
+						/*
+						 * No more inner tuples.  However, this might be
+						 * only effective and not physical end of inner plan,
+						 * so force mj_InnerTupleSlot to null to make sure we
+						 * don't fetch more inner tuples.  (We need this hack
+						 * because we are not transiting to a state where the
+						 * inner plan is assumed to be exhausted.)
+						 */
+						node->mj_InnerTupleSlot = NULL;
+						node->mj_JoinState = EXEC_MJ_NEXTOUTER;
+						break;
 				}
 				break;
 
@@ -962,37 +1012,32 @@ ExecMergeJoin(MergeJoinState *node)
 				MJ_DEBUG_PROC_NODE(outerTupleSlot);
 				node->mj_MatchedOuter = false;
 
-				/*
-				 * if the outer tuple is null then we are done with the join,
-				 * unless we have inner tuples we need to null-fill.
-				 */
-				if (TupIsNull(outerTupleSlot))
-				{
-					MJ_printf("ExecMergeJoin: end of outer subplan\n");
-					innerTupleSlot = node->mj_InnerTupleSlot;
-					if (doFillInner && !TupIsNull(innerTupleSlot))
-					{
-						/*
-						 * Need to emit right-join tuples for remaining inner
-						 * tuples.
-						 */
-						node->mj_JoinState = EXEC_MJ_ENDOUTER;
-						break;
-					}
-					/* Otherwise we're done. */
-					return NULL;
-				}
-
 				/* Compute join values and check for unmatchability */
-				if (MJEvalOuterValues(node))
+				switch (MJEvalOuterValues(node))
 				{
-					/* Go test the new tuple against the marked tuple */
-					node->mj_JoinState = EXEC_MJ_TESTOUTER;
-				}
-				else
-				{
-					/* Can't match, so fetch next outer tuple */
-					node->mj_JoinState = EXEC_MJ_NEXTOUTER;
+					case MJEVAL_MATCHABLE:
+						/* Go test the new tuple against the marked tuple */
+						node->mj_JoinState = EXEC_MJ_TESTOUTER;
+						break;
+					case MJEVAL_NONMATCHABLE:
+						/* Can't match, so fetch next outer tuple */
+						node->mj_JoinState = EXEC_MJ_NEXTOUTER;
+						break;
+					case MJEVAL_ENDOFJOIN:
+						/* No more outer tuples */
+						MJ_printf("ExecMergeJoin: end of outer subplan\n");
+						innerTupleSlot = node->mj_InnerTupleSlot;
+						if (doFillInner && !TupIsNull(innerTupleSlot))
+						{
+							/*
+							 * Need to emit right-join tuples for remaining
+							 * inner tuples.
+							 */
+							node->mj_JoinState = EXEC_MJ_ENDOUTER;
+							break;
+						}
+						/* Otherwise we're done. */
+						return NULL;
 				}
 				break;
 
@@ -1093,39 +1138,39 @@ ExecMergeJoin(MergeJoinState *node)
 					 *	larger than our marked inner tuples.  So we need not
 					 *	revisit any of the marked tuples but can proceed to
 					 *	look for a match to the current inner.	If there's
-					 *	no more inners, we are done.
+					 *	no more inners, no more matches are possible.
 					 * ----------------
 					 */
 					Assert(compareResult > 0);
 					innerTupleSlot = node->mj_InnerTupleSlot;
-					if (TupIsNull(innerTupleSlot))
-					{
-						if (doFillOuter)
-						{
-							/*
-							 * Need to emit left-join tuples for remaining
-							 * outer tuples.
-							 */
-							node->mj_JoinState = EXEC_MJ_ENDINNER;
-							break;
-						}
-						/* Otherwise we're done. */
-						return NULL;
-					}
 
 					/* reload comparison data for current inner */
-					if (MJEvalInnerValues(node, innerTupleSlot))
+					switch (MJEvalInnerValues(node, innerTupleSlot))
 					{
-						/* proceed to compare it to the current outer */
-						node->mj_JoinState = EXEC_MJ_SKIP_TEST;
-					}
-					else
-					{
-						/*
-						 * current inner can't possibly match any outer;
-						 * better to advance the inner scan than the outer.
-						 */
-						node->mj_JoinState = EXEC_MJ_SKIPINNER_ADVANCE;
+						case MJEVAL_MATCHABLE:
+							/* proceed to compare it to the current outer */
+							node->mj_JoinState = EXEC_MJ_SKIP_TEST;
+							break;
+						case MJEVAL_NONMATCHABLE:
+							/*
+							 * current inner can't possibly match any outer;
+							 * better to advance the inner scan than the outer.
+							 */
+							node->mj_JoinState = EXEC_MJ_SKIPINNER_ADVANCE;
+							break;
+						case MJEVAL_ENDOFJOIN:
+							/* No more inner tuples */
+							if (doFillOuter)
+							{
+								/*
+								 * Need to emit left-join tuples for remaining
+								 * outer tuples.
+								 */
+								node->mj_JoinState = EXEC_MJ_ENDINNER;
+								break;
+							}
+							/* Otherwise we're done. */
+							return NULL;
 					}
 				}
 				break;
@@ -1218,37 +1263,32 @@ ExecMergeJoin(MergeJoinState *node)
 				MJ_DEBUG_PROC_NODE(outerTupleSlot);
 				node->mj_MatchedOuter = false;
 
-				/*
-				 * if the outer tuple is null then we are done with the join,
-				 * unless we have inner tuples we need to null-fill.
-				 */
-				if (TupIsNull(outerTupleSlot))
-				{
-					MJ_printf("ExecMergeJoin: end of outer subplan\n");
-					innerTupleSlot = node->mj_InnerTupleSlot;
-					if (doFillInner && !TupIsNull(innerTupleSlot))
-					{
-						/*
-						 * Need to emit right-join tuples for remaining inner
-						 * tuples.
-						 */
-						node->mj_JoinState = EXEC_MJ_ENDOUTER;
-						break;
-					}
-					/* Otherwise we're done. */
-					return NULL;
-				}
-
 				/* Compute join values and check for unmatchability */
-				if (MJEvalOuterValues(node))
+				switch (MJEvalOuterValues(node))
 				{
-					/* Go test the new tuple against the current inner */
-					node->mj_JoinState = EXEC_MJ_SKIP_TEST;
-				}
-				else
-				{
-					/* Can't match, so fetch next outer tuple */
-					node->mj_JoinState = EXEC_MJ_SKIPOUTER_ADVANCE;
+					case MJEVAL_MATCHABLE:
+						/* Go test the new tuple against the current inner */
+						node->mj_JoinState = EXEC_MJ_SKIP_TEST;
+						break;
+					case MJEVAL_NONMATCHABLE:
+						/* Can't match, so fetch next outer tuple */
+						node->mj_JoinState = EXEC_MJ_SKIPOUTER_ADVANCE;
+						break;
+					case MJEVAL_ENDOFJOIN:
+						/* No more outer tuples */
+						MJ_printf("ExecMergeJoin: end of outer subplan\n");
+						innerTupleSlot = node->mj_InnerTupleSlot;
+						if (doFillInner && !TupIsNull(innerTupleSlot))
+						{
+							/*
+							 * Need to emit right-join tuples for remaining
+							 * inner tuples.
+							 */
+							node->mj_JoinState = EXEC_MJ_ENDOUTER;
+							break;
+						}
+						/* Otherwise we're done. */
+						return NULL;
 				}
 				break;
 
@@ -1289,40 +1329,35 @@ ExecMergeJoin(MergeJoinState *node)
 				MJ_DEBUG_PROC_NODE(innerTupleSlot);
 				node->mj_MatchedInner = false;
 
-				/*
-				 * if the inner tuple is null then we are done with the join,
-				 * unless we have outer tuples we need to null-fill.
-				 */
-				if (TupIsNull(innerTupleSlot))
-				{
-					MJ_printf("ExecMergeJoin: end of inner subplan\n");
-					outerTupleSlot = node->mj_OuterTupleSlot;
-					if (doFillOuter && !TupIsNull(outerTupleSlot))
-					{
-						/*
-						 * Need to emit left-join tuples for remaining outer
-						 * tuples.
-						 */
-						node->mj_JoinState = EXEC_MJ_ENDINNER;
-						break;
-					}
-					/* Otherwise we're done. */
-					return NULL;
-				}
-
 				/* Compute join values and check for unmatchability */
-				if (MJEvalInnerValues(node, innerTupleSlot))
+				switch (MJEvalInnerValues(node, innerTupleSlot))
 				{
-					/* proceed to compare it to the current outer */
-					node->mj_JoinState = EXEC_MJ_SKIP_TEST;
-				}
-				else
-				{
-					/*
-					 * current inner can't possibly match any outer; better to
-					 * advance the inner scan than the outer.
-					 */
-					node->mj_JoinState = EXEC_MJ_SKIPINNER_ADVANCE;
+					case MJEVAL_MATCHABLE:
+						/* proceed to compare it to the current outer */
+						node->mj_JoinState = EXEC_MJ_SKIP_TEST;
+						break;
+					case MJEVAL_NONMATCHABLE:
+						/*
+						 * current inner can't possibly match any outer;
+						 * better to advance the inner scan than the outer.
+						 */
+						node->mj_JoinState = EXEC_MJ_SKIPINNER_ADVANCE;
+						break;
+					case MJEVAL_ENDOFJOIN:
+						/* No more inner tuples */
+						MJ_printf("ExecMergeJoin: end of inner subplan\n");
+						outerTupleSlot = node->mj_OuterTupleSlot;
+						if (doFillOuter && !TupIsNull(outerTupleSlot))
+						{
+							/*
+							 * Need to emit left-join tuples for remaining
+							 * outer tuples.
+							 */
+							node->mj_JoinState = EXEC_MJ_ENDINNER;
+							break;
+						}
+						/* Otherwise we're done. */
+						return NULL;
 				}
 				break;