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.

Author: tglsfdc

src/backend/executor/execQual.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/execQual.c,v 1.243 2009/03/27 18:30:21 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/execQual.c,v 1.244 2009/04/02 22:39:29 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -4966,6 +4966,7 @@ ExecCleanTargetListLength(List *targetlist)
  * prepared to deal with sets of result tuples.  Otherwise, a return
  * of *isDone = ExprMultipleResult signifies a set element, and a return
  * of *isDone = ExprEndResult signifies end of the set of tuple.
+ * We assume that *isDone has been initialized to ExprSingleResult by caller.
  */
 static bool
 ExecTargetList(List *targetlist,
@@ -4987,9 +4988,6 @@ ExecTargetList(List *targetlist,
 	/*
 	 * evaluate all the expressions in the target list
 	 */
-	if (isDone)
-		*isDone = ExprSingleResult;		/* until proven otherwise */
-
 	haveDoneSets = false;		/* any exhausted set exprs in tlist? */
 
 	foreach(tl, targetlist)
@@ -5104,50 +5102,6 @@ ExecTargetList(List *targetlist,
 	return true;
 }
 
-/*
- * ExecVariableList
- *		Evaluates a simple-Variable-list projection.
- *
- * Results are stored into the passed values and isnull arrays.
- */
-static void
-ExecVariableList(ProjectionInfo *projInfo,
-				 Datum *values,
-				 bool *isnull)
-{
-	ExprContext *econtext = projInfo->pi_exprContext;
-	int		   *varSlotOffsets = projInfo->pi_varSlotOffsets;
-	int		   *varNumbers = projInfo->pi_varNumbers;
-	int			i;
-
-	/*
-	 * Force extraction of all input values that we need.
-	 */
-	if (projInfo->pi_lastInnerVar > 0)
-		slot_getsomeattrs(econtext->ecxt_innertuple,
-						  projInfo->pi_lastInnerVar);
-	if (projInfo->pi_lastOuterVar > 0)
-		slot_getsomeattrs(econtext->ecxt_outertuple,
-						  projInfo->pi_lastOuterVar);
-	if (projInfo->pi_lastScanVar > 0)
-		slot_getsomeattrs(econtext->ecxt_scantuple,
-						  projInfo->pi_lastScanVar);
-
-	/*
-	 * Assign to result by direct extraction of fields from source slots ... a
-	 * mite ugly, but fast ...
-	 */
-	for (i = list_length(projInfo->pi_targetlist) - 1; i >= 0; i--)
-	{
-		char	   *slotptr = ((char *) econtext) + varSlotOffsets[i];
-		TupleTableSlot *varSlot = *((TupleTableSlot **) slotptr);
-		int			varNumber = varNumbers[i] - 1;
-
-		values[i] = varSlot->tts_values[varNumber];
-		isnull[i] = varSlot->tts_isnull[varNumber];
-	}
-}
-
 /*
  * ExecProject
  *
@@ -5165,6 +5119,8 @@ TupleTableSlot *
 ExecProject(ProjectionInfo *projInfo, ExprDoneCond *isDone)
 {
 	TupleTableSlot *slot;
+	ExprContext *econtext;
+	int			numSimpleVars;
 
 	/*
 	 * sanity checks
@@ -5175,6 +5131,11 @@ ExecProject(ProjectionInfo *projInfo, ExprDoneCond *isDone)
 	 * get the projection info we want
 	 */
 	slot = projInfo->pi_slot;
+	econtext = projInfo->pi_exprContext;
+
+	/* Assume single result row until proven otherwise */
+	if (isDone)
+		*isDone = ExprSingleResult;
 
 	/*
 	 * Clear any former contents of the result slot.  This makes it safe for
@@ -5184,29 +5145,84 @@ ExecProject(ProjectionInfo *projInfo, ExprDoneCond *isDone)
 	ExecClearTuple(slot);
 
 	/*
-	 * form a new result tuple (if possible); if successful, mark the result
-	 * slot as containing a valid virtual tuple
+	 * Force extraction of all input values that we'll need.  The
+	 * Var-extraction loops below depend on this, and we are also prefetching
+	 * all attributes that will be referenced in the generic expressions.
+	 */
+	if (projInfo->pi_lastInnerVar > 0)
+		slot_getsomeattrs(econtext->ecxt_innertuple,
+						  projInfo->pi_lastInnerVar);
+	if (projInfo->pi_lastOuterVar > 0)
+		slot_getsomeattrs(econtext->ecxt_outertuple,
+						  projInfo->pi_lastOuterVar);
+	if (projInfo->pi_lastScanVar > 0)
+		slot_getsomeattrs(econtext->ecxt_scantuple,
+						  projInfo->pi_lastScanVar);
+
+	/*
+	 * Assign simple Vars to result by direct extraction of fields from source
+	 * slots ... a mite ugly, but fast ...
 	 */
-	if (projInfo->pi_isVarList)
+	numSimpleVars = projInfo->pi_numSimpleVars;
+	if (numSimpleVars > 0)
 	{
-		/* simple Var list: this always succeeds with one result row */
-		if (isDone)
-			*isDone = ExprSingleResult;
-		ExecVariableList(projInfo,
-						 slot->tts_values,
-						 slot->tts_isnull);
-		ExecStoreVirtualTuple(slot);
+		Datum  *values = slot->tts_values;
+		bool   *isnull = slot->tts_isnull;
+		int	   *varSlotOffsets = projInfo->pi_varSlotOffsets;
+		int	   *varNumbers = projInfo->pi_varNumbers;
+		int		i;
+
+		if (projInfo->pi_directMap)
+		{
+			/* especially simple case where vars go to output in order */
+			for (i = 0; i < numSimpleVars; i++)
+			{
+				char	   *slotptr = ((char *) econtext) + varSlotOffsets[i];
+				TupleTableSlot *varSlot = *((TupleTableSlot **) slotptr);
+				int			varNumber = varNumbers[i] - 1;
+
+				values[i] = varSlot->tts_values[varNumber];
+				isnull[i] = varSlot->tts_isnull[varNumber];
+			}
+		}
+		else
+		{
+			/* we have to pay attention to varOutputCols[] */
+			int	   *varOutputCols = projInfo->pi_varOutputCols;
+
+			for (i = 0; i < numSimpleVars; i++)
+			{
+				char	   *slotptr = ((char *) econtext) + varSlotOffsets[i];
+				TupleTableSlot *varSlot = *((TupleTableSlot **) slotptr);
+				int			varNumber = varNumbers[i] - 1;
+				int			varOutputCol = varOutputCols[i] - 1;
+
+				values[varOutputCol] = varSlot->tts_values[varNumber];
+				isnull[varOutputCol] = varSlot->tts_isnull[varNumber];
+			}
+		}
 	}
-	else
+
+	/*
+	 * If there are any generic expressions, evaluate them.  It's possible
+	 * that there are set-returning functions in such expressions; if so
+	 * and we have reached the end of the set, we return the result slot,
+	 * which we already marked empty.
+	 */
+	if (projInfo->pi_targetlist)
 	{
-		if (ExecTargetList(projInfo->pi_targetlist,
-						   projInfo->pi_exprContext,
-						   slot->tts_values,
-						   slot->tts_isnull,
-						   projInfo->pi_itemIsDone,
-						   isDone))
-			ExecStoreVirtualTuple(slot);
+		if (!ExecTargetList(projInfo->pi_targetlist,
+							econtext,
+							slot->tts_values,
+							slot->tts_isnull,
+							projInfo->pi_itemIsDone,
+							isDone))
+			return slot;		/* no more result rows, return empty slot */
 	}
 
-	return slot;
+	/*
+	 * Successfully formed a result row.  Mark the result slot as containing a
+	 * valid virtual tuple.
+	 */
+	return ExecStoreVirtualTuple(slot);
 }