*** pgsql/src/backend/optimizer/plan/createplan.c	2009/01/01 17:23:44	1.255
--- pgsql/src/backend/optimizer/plan/createplan.c	2009/03/21 00:04:39	1.256
***************
*** 10,16 ****
   *
   *
   * IDENTIFICATION
!  *	  $PostgreSQL: pgsql/src/backend/optimizer/plan/createplan.c,v 1.254 2008/12/31 00:08:36 tgl Exp $
   *
   *-------------------------------------------------------------------------
   */
--- 10,16 ----
   *
   *
   * IDENTIFICATION
!  *	  $PostgreSQL: pgsql/src/backend/optimizer/plan/createplan.c,v 1.255 2009/01/01 17:23:44 momjian Exp $
   *
   *-------------------------------------------------------------------------
   */
*************** static HashJoin *make_hashjoin(List *tli
*** 112,118 ****
  			  List *hashclauses,
  			  Plan *lefttree, Plan *righttree,
  			  JoinType jointype);
! static Hash *make_hash(Plan *lefttree);
  static MergeJoin *make_mergejoin(List *tlist,
  			   List *joinclauses, List *otherclauses,
  			   List *mergeclauses,
--- 112,122 ----
  			  List *hashclauses,
  			  Plan *lefttree, Plan *righttree,
  			  JoinType jointype);
! static Hash *make_hash(Plan *lefttree,
! 					   Oid skewTable,
! 					   AttrNumber skewColumn,
! 					   Oid skewColType,
! 					   int32 skewColTypmod);
  static MergeJoin *make_mergejoin(List *tlist,
  			   List *joinclauses, List *otherclauses,
  			   List *mergeclauses,
*************** create_hashjoin_plan(PlannerInfo *root,
*** 1864,1869 ****
--- 1868,1877 ----
  	List	   *joinclauses;
  	List	   *otherclauses;
  	List	   *hashclauses;
+ 	Oid			skewTable = InvalidOid;
+ 	AttrNumber	skewColumn = InvalidAttrNumber;
+ 	Oid			skewColType = InvalidOid;
+ 	int32		skewColTypmod = -1;
  	HashJoin   *join_plan;
  	Hash	   *hash_plan;
  
*************** create_hashjoin_plan(PlannerInfo *root,
*** 1903,1911 ****
  	disuse_physical_tlist(inner_plan, best_path->jpath.innerjoinpath);
  
  	/*
  	 * Build the hash node and hash join node.
  	 */
! 	hash_plan = make_hash(inner_plan);
  	join_plan = make_hashjoin(tlist,
  							  joinclauses,
  							  otherclauses,
--- 1911,1956 ----
  	disuse_physical_tlist(inner_plan, best_path->jpath.innerjoinpath);
  
  	/*
+ 	 * If there is a single join clause and we can identify the outer
+ 	 * variable as a simple column reference, supply its identity for
+ 	 * possible use in skew optimization.  (Note: in principle we could
+ 	 * do skew optimization with multiple join clauses, but we'd have to
+ 	 * be able to determine the most common combinations of outer values,
+ 	 * which we don't currently have enough stats for.)
+ 	 */
+ 	if (list_length(hashclauses) == 1)
+ 	{
+ 		OpExpr	   *clause = (OpExpr *) linitial(hashclauses);
+ 		Node	   *node;
+ 
+ 		Assert(is_opclause(clause));
+ 		node = (Node *) linitial(clause->args);
+ 		if (IsA(node, RelabelType))
+ 			node = (Node *) ((RelabelType *) node)->arg;
+ 		if (IsA(node, Var))
+ 		{
+ 			Var	   *var = (Var *) node;
+ 			RangeTblEntry *rte;
+ 
+ 			rte = root->simple_rte_array[var->varno];
+ 			if (rte->rtekind == RTE_RELATION)
+ 			{
+ 				skewTable = rte->relid;
+ 				skewColumn = var->varattno;
+ 				skewColType = var->vartype;
+ 				skewColTypmod = var->vartypmod;
+ 			}
+ 		}
+ 	}
+ 
+ 	/*
  	 * Build the hash node and hash join node.
  	 */
! 	hash_plan = make_hash(inner_plan,
! 						  skewTable,
! 						  skewColumn,
! 						  skewColType,
! 						  skewColTypmod);
  	join_plan = make_hashjoin(tlist,
  							  joinclauses,
  							  otherclauses,
*************** make_hashjoin(List *tlist,
*** 2713,2719 ****
  }
  
  static Hash *
! make_hash(Plan *lefttree)
  {
  	Hash	   *node = makeNode(Hash);
  	Plan	   *plan = &node->plan;
--- 2758,2768 ----
  }
  
  static Hash *
! make_hash(Plan *lefttree,
! 		  Oid skewTable,
! 		  AttrNumber skewColumn,
! 		  Oid skewColType,
! 		  int32 skewColTypmod)
  {
  	Hash	   *node = makeNode(Hash);
  	Plan	   *plan = &node->plan;
*************** make_hash(Plan *lefttree)
*** 2730,2735 ****
--- 2779,2789 ----
  	plan->lefttree = lefttree;
  	plan->righttree = NULL;
  
+ 	node->skewTable = skewTable;
+ 	node->skewColumn = skewColumn;
+ 	node->skewColType = skewColType;
+ 	node->skewColTypmod = skewColTypmod;
+ 
  	return node;
  }