Index: src/backend/optimizer/path/clausesel.c
===================================================================
RCS file: /cvsroot/pgsql/src/backend/optimizer/path/clausesel.c,v
retrieving revision 1.82
diff -c -r1.82 clausesel.c
*** src/backend/optimizer/path/clausesel.c	4 Oct 2006 00:29:53 -0000	1.82
--- src/backend/optimizer/path/clausesel.c	31 Aug 2007 23:29:01 -0000
***************
*** 218,224 ****
  				s2 = rqlist->hibound + rqlist->lobound - 1.0;
  
  				/* Adjust for double-exclusion of NULLs */
! 				s2 += nulltestsel(root, IS_NULL, rqlist->var, varRelid);
  
  				/*
  				 * A zero or slightly negative s2 should be converted into a
--- 218,226 ----
  				s2 = rqlist->hibound + rqlist->lobound - 1.0;
  
  				/* Adjust for double-exclusion of NULLs */
! 				/* HACK: disable nulltestsel's special outer-join logic */
! 				s2 += nulltestsel(root, IS_NULL, rqlist->var,
! 								  varRelid, JOIN_INNER);
  
  				/*
  				 * A zero or slightly negative s2 should be converted into a
***************
*** 701,707 ****
  		s1 = nulltestsel(root,
  						 ((NullTest *) clause)->nulltesttype,
  						 (Node *) ((NullTest *) clause)->arg,
! 						 varRelid);
  	}
  	else if (IsA(clause, BooleanTest))
  	{
--- 703,710 ----
  		s1 = nulltestsel(root,
  						 ((NullTest *) clause)->nulltesttype,
  						 (Node *) ((NullTest *) clause)->arg,
! 						 varRelid,
! 						 jointype);
  	}
  	else if (IsA(clause, BooleanTest))
  	{
Index: src/backend/utils/adt/selfuncs.c
===================================================================
RCS file: /cvsroot/pgsql/src/backend/utils/adt/selfuncs.c,v
retrieving revision 1.214.2.5
diff -c -r1.214.2.5 selfuncs.c
*** src/backend/utils/adt/selfuncs.c	5 May 2007 17:05:55 -0000	1.214.2.5
--- src/backend/utils/adt/selfuncs.c	31 Aug 2007 23:29:02 -0000
***************
*** 1386,1396 ****
   */
  Selectivity
  nulltestsel(PlannerInfo *root, NullTestType nulltesttype,
! 			Node *arg, int varRelid)
  {
  	VariableStatData vardata;
  	double		selec;
  
  	examine_variable(root, arg, varRelid, &vardata);
  
  	if (HeapTupleIsValid(vardata.statsTuple))
--- 1386,1409 ----
   */
  Selectivity
  nulltestsel(PlannerInfo *root, NullTestType nulltesttype,
! 			Node *arg, int varRelid, JoinType jointype)
  {
  	VariableStatData vardata;
  	double		selec;
  
+ 	/*
+ 	 * Special hack: an IS NULL test being applied at an outer join should not
+ 	 * be taken at face value, since it's very likely being used to select the
+ 	 * outer-side rows that don't have a match, and thus its selectivity has
+ 	 * nothing whatever to do with the statistics of the original table
+ 	 * column.  We do not have nearly enough context here to determine its
+ 	 * true selectivity, so for the moment punt and guess at 0.5.  Eventually
+ 	 * the planner should be made to provide enough info about the clause's
+ 	 * context to let us do better.
+ 	 */
+ 	if (IS_OUTER_JOIN(jointype) && nulltesttype == IS_NULL)
+ 		return (Selectivity) 0.5;
+ 
  	examine_variable(root, arg, varRelid, &vardata);
  
  	if (HeapTupleIsValid(vardata.statsTuple))
Index: src/include/utils/selfuncs.h
===================================================================
RCS file: /cvsroot/pgsql/src/include/utils/selfuncs.h,v
retrieving revision 1.36
diff -c -r1.36 selfuncs.h
*** src/include/utils/selfuncs.h	4 Oct 2006 00:30:11 -0000	1.36
--- src/include/utils/selfuncs.h	31 Aug 2007 23:29:02 -0000
***************
*** 149,155 ****
  extern Selectivity booltestsel(PlannerInfo *root, BoolTestType booltesttype,
  			Node *arg, int varRelid, JoinType jointype);
  extern Selectivity nulltestsel(PlannerInfo *root, NullTestType nulltesttype,
! 			Node *arg, int varRelid);
  extern Selectivity scalararraysel(PlannerInfo *root,
  			   ScalarArrayOpExpr *clause,
  			   bool is_join_clause,
--- 149,155 ----
  extern Selectivity booltestsel(PlannerInfo *root, BoolTestType booltesttype,
  			Node *arg, int varRelid, JoinType jointype);
  extern Selectivity nulltestsel(PlannerInfo *root, NullTestType nulltesttype,
! 			Node *arg, int varRelid, JoinType jointype);
  extern Selectivity scalararraysel(PlannerInfo *root,
  			   ScalarArrayOpExpr *clause,
  			   bool is_join_clause,