Refactor ExecProject and associated routines so that fast-path code is used

for simple Var targetlist entries all the time, even when there are other
entries that are not simple Vars.  Also, ensure that we prefetch attributes
(with slot_getsomeattrs) for all Vars in the targetlist, even those buried
within expressions.  In combination these changes seem to significantly
reduce the runtime for cases where tlists are mostly but not exclusively
Vars.  Per my proposal of yesterday.

1 files changed, 19 insertions, 8 deletions

diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 996efa8f87d..cb293a0be55 100644
--- a/src/include/nodes/execnodes.h
+++ b/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 1.202 2009/03/21 00:04:40 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/nodes/execnodes.h,v 1.203 2009/04/02 22:39:30 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -201,16 +201,25 @@ typedef struct ReturnSetInfo
  *
  *		The planner very often produces tlists that consist entirely of
  *		simple Var references (lower levels of a plan tree almost always
- *		look like that).  So we have an optimization to handle that case
- *		with minimum overhead.
+ *		look like that).  And top-level tlists are often mostly Vars too.
+ *		We therefore optimize execution of simple-Var tlist entries.
+ *		The pi_targetlist list actually contains only the tlist entries that
+ *		aren't simple Vars, while those that are Vars are processed using the
+ *		varSlotOffsets/varNumbers/varOutputCols arrays.
  *
- *		targetlist		target list for projection
+ *		The lastXXXVar fields are used to optimize fetching of fields from
+ *		input tuples: they let us do a slot_getsomeattrs() call to ensure
+ *		that all needed attributes are extracted in one pass.
+ *
+ *		targetlist		target list for projection (non-Var expressions only)
  *		exprContext		expression context in which to evaluate targetlist
  *		slot			slot to place projection result in
- *		itemIsDone		workspace for ExecProject
- *		isVarList		TRUE if simple-Var-list optimization applies
+ *		itemIsDone		workspace array for ExecProject
+ *		directMap		true if varOutputCols[] is an identity map
+ *		numSimpleVars	number of simple Vars found in original tlist
  *		varSlotOffsets	array indicating which slot each simple Var is from
- *		varNumbers		array indicating attr numbers of simple Vars
+ *		varNumbers		array containing input attr numbers of simple Vars
+ *		varOutputCols	array containing output attr numbers of simple Vars
  *		lastInnerVar	highest attnum from inner tuple slot (0 if none)
  *		lastOuterVar	highest attnum from outer tuple slot (0 if none)
  *		lastScanVar		highest attnum from scan tuple slot (0 if none)
@@ -223,9 +232,11 @@ typedef struct ProjectionInfo
 	ExprContext *pi_exprContext;
 	TupleTableSlot *pi_slot;
 	ExprDoneCond *pi_itemIsDone;
-	bool		pi_isVarList;
+	bool		pi_directMap;
+	int			pi_numSimpleVars;
 	int		   *pi_varSlotOffsets;
 	int		   *pi_varNumbers;
+	int		   *pi_varOutputCols;
 	int			pi_lastInnerVar;
 	int			pi_lastOuterVar;
 	int			pi_lastScanVar;