Refactor ExecGetJunkAttribute to avoid searching for junk attributes

by name on each and every row processed.  Profiling suggests this may
buy a percent or two for simple UPDATE scenarios, which isn't huge,
but when it's so easy to get ...

src/backend/executor/execJunk.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/execJunk.c,v 1.54 2006/07/14 14:52:18 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/execJunk.c,v 1.55 2006/12/04 02:06:55 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -26,24 +26,25 @@
  * never make it out of the executor, i.e. they are never printed,
  * returned or stored on disk. Their only purpose in life is to
  * store some information useful only to the executor, mainly the values
- * of some system attributes like "ctid" or rule locks.
+ * of system attributes like "ctid", or sort key columns that are not to
+ * be output.
  *
  * The general idea is the following: A target list consists of a list of
  * TargetEntry nodes containing expressions. Each TargetEntry has a field
  * called 'resjunk'. If the value of this field is true then the
  * corresponding attribute is a "junk" attribute.
  *
- * When we initialize a plan we call 'ExecInitJunkFilter' to create
- * and store the appropriate information in the 'es_junkFilter' attribute of
+ * When we initialize a plan we call ExecInitJunkFilter to create
+ * and store the appropriate information in the es_junkFilter attribute of
  * EState.
  *
- * We then execute the plan ignoring the "resjunk" attributes.
+ * We then execute the plan, treating the resjunk attributes like any others.
  *
  * Finally, when at the top level we get back a tuple, we can call
- * ExecGetJunkAttribute to retrieve the value of the junk attributes we
- * are interested in, and ExecFilterJunk or ExecRemoveJunk to remove all
- * the junk attributes from a tuple. This new "clean" tuple is then printed,
- * replaced, deleted or inserted.
+ * ExecFindJunkAttribute/ExecGetJunkAttribute to retrieve the values of the
+ * junk attributes we are interested in, and ExecFilterJunk or ExecRemoveJunk
+ * to remove all the junk attributes from a tuple. This new "clean" tuple is
+ * then printed, replaced, deleted or inserted.
  *
  *-------------------------------------------------------------------------
  */
@@ -201,26 +202,16 @@ ExecInitJunkFilterConversion(List *targetList,
 }
 
 /*
- * ExecGetJunkAttribute
- *
- * Given a tuple (slot), the junk filter and a junk attribute's name,
- * extract & return the value and isNull flag of this attribute.
+ * ExecFindJunkAttribute
  *
- * It returns false iff no junk attribute with such name was found.
+ * Locate the specified junk attribute in the junk filter's targetlist,
+ * and return its resno.  Returns InvalidAttrNumber if not found.
  */
-bool
-ExecGetJunkAttribute(JunkFilter *junkfilter,
-					 TupleTableSlot *slot,
-					 char *attrName,
-					 Datum *value,
-					 bool *isNull)
+AttrNumber
+ExecFindJunkAttribute(JunkFilter *junkfilter, const char *attrName)
 {
 	ListCell   *t;
 
-	/*
-	 * Look in the junkfilter's target list for an attribute with the given
-	 * name
-	 */
 	foreach(t, junkfilter->jf_targetList)
 	{
 		TargetEntry *tle = lfirst(t);
@@ -229,13 +220,27 @@ ExecGetJunkAttribute(JunkFilter *junkfilter,
 			(strcmp(tle->resname, attrName) == 0))
 		{
 			/* We found it ! */
-			*value = slot_getattr(slot, tle->resno, isNull);
-			return true;
+			return tle->resno;
 		}
 	}
 
-	/* Ooops! We couldn't find this attribute... */
-	return false;
+	return InvalidAttrNumber;
+}
+
+/*
+ * ExecGetJunkAttribute
+ *
+ * Given a junk filter's input tuple (slot) and a junk attribute's number
+ * previously found by ExecFindJunkAttribute, extract & return the value and
+ * isNull flag of the attribute.
+ */
+Datum
+ExecGetJunkAttribute(TupleTableSlot *slot, AttrNumber attno,
+					 bool *isNull)
+{
+	Assert(attno > 0);
+
+	return slot_getattr(slot, attno, isNull);
 }
 
 /*

src/backend/executor/execMain.c

@@ -26,7 +26,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/execMain.c,v 1.280 2006/10/04 00:29:52 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/execMain.c,v 1.281 2006/12/04 02:06:55 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -567,7 +567,9 @@ InitPlan(QueryDesc *queryDesc, int eflags)
 	}
 
 	/*
-	 * Have to lock relations selected FOR UPDATE/FOR SHARE
+	 * Have to lock relations selected FOR UPDATE/FOR SHARE before we
+	 * initialize the plan tree, else we'd be doing a lock upgrade.
+	 * While we are at it, build the ExecRowMark list.
 	 */
 	estate->es_rowMarks = NIL;
 	foreach(l, parseTree->rowMarks)
@@ -583,7 +585,8 @@ InitPlan(QueryDesc *queryDesc, int eflags)
 		erm->rti = rc->rti;
 		erm->forUpdate = rc->forUpdate;
 		erm->noWait = rc->noWait;
-		snprintf(erm->resname, sizeof(erm->resname), "ctid%u", rc->rti);
+		/* We'll set up ctidAttno below */
+		erm->ctidAttNo = InvalidAttrNumber;
 		estate->es_rowMarks = lappend(estate->es_rowMarks, erm);
 	}
 
@@ -703,6 +706,16 @@ InitPlan(QueryDesc *queryDesc, int eflags)
 					j = ExecInitJunkFilter(subplan->plan->targetlist,
 							resultRelInfo->ri_RelationDesc->rd_att->tdhasoid,
 								  ExecAllocTableSlot(estate->es_tupleTable));
+					/*
+					 * Since it must be UPDATE/DELETE, there had better be
+					 * a "ctid" junk attribute in the tlist ... but ctid could
+					 * be at a different resno for each result relation.
+					 * We look up the ctid resnos now and save them in the
+					 * junkfilters.
+					 */
+					j->jf_junkAttNo = ExecFindJunkAttribute(j, "ctid");
+					if (!AttributeNumberIsValid(j->jf_junkAttNo))
+						elog(ERROR, "could not find junk ctid column");
 					resultRelInfo->ri_junkFilter = j;
 					resultRelInfo++;
 				}
@@ -726,9 +739,30 @@ InitPlan(QueryDesc *queryDesc, int eflags)
 				if (estate->es_result_relation_info)
 					estate->es_result_relation_info->ri_junkFilter = j;
 
-				/* For SELECT, want to return the cleaned tuple type */
 				if (operation == CMD_SELECT)
+				{
+					/* For SELECT, want to return the cleaned tuple type */
 					tupType = j->jf_cleanTupType;
+					/* For SELECT FOR UPDATE/SHARE, find the ctid attrs now */
+					foreach(l, estate->es_rowMarks)
+					{
+						ExecRowMark *erm = (ExecRowMark *) lfirst(l);
+						char		resname[32];
+
+						snprintf(resname, sizeof(resname), "ctid%u", erm->rti);
+						erm->ctidAttNo = ExecFindJunkAttribute(j, resname);
+						if (!AttributeNumberIsValid(erm->ctidAttNo))
+							elog(ERROR, "could not find junk \"%s\" column",
+								 resname);
+					}
+				}
+				else if (operation == CMD_UPDATE || operation == CMD_DELETE)
+				{
+					/* For UPDATE/DELETE, find the ctid junk attr now */
+					j->jf_junkAttNo = ExecFindJunkAttribute(j, "ctid");
+					if (!AttributeNumberIsValid(j->jf_junkAttNo))
+						elog(ERROR, "could not find junk ctid column");
+				}
 			}
 		}
 		else
@@ -1111,13 +1145,8 @@ lnext:	;
 			 */
 			if (operation == CMD_UPDATE || operation == CMD_DELETE)
 			{
-				if (!ExecGetJunkAttribute(junkfilter,
-										  slot,
-										  "ctid",
-										  &datum,
-										  &isNull))
-					elog(ERROR, "could not find junk ctid column");
-
+				datum = ExecGetJunkAttribute(slot, junkfilter->jf_junkAttNo,
+											 &isNull);
 				/* shouldn't ever get a null result... */
 				if (isNull)
 					elog(ERROR, "ctid is NULL");
@@ -1146,17 +1175,12 @@ lnext:	;
 					LockTupleMode lockmode;
 					HTSU_Result test;
 
-					if (!ExecGetJunkAttribute(junkfilter,
-											  slot,
-											  erm->resname,
-											  &datum,
-											  &isNull))
-						elog(ERROR, "could not find junk \"%s\" column",
-							 erm->resname);
-
+					datum = ExecGetJunkAttribute(slot,
+												 erm->ctidAttNo,
+												 &isNull);
 					/* shouldn't ever get a null result... */
 					if (isNull)
-						elog(ERROR, "\"%s\" is NULL", erm->resname);
+						elog(ERROR, "ctid is NULL");
 
 					tuple.t_self = *((ItemPointer) DatumGetPointer(datum));
 

src/include/executor/executor.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/executor/executor.h,v 1.130 2006/10/04 00:30:08 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/executor/executor.h,v 1.131 2006/12/04 02:06:55 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -110,8 +110,10 @@ extern JunkFilter *ExecInitJunkFilter(List *targetList, bool hasoid,
 extern JunkFilter *ExecInitJunkFilterConversion(List *targetList,
 							 TupleDesc cleanTupType,
 							 TupleTableSlot *slot);
-extern bool ExecGetJunkAttribute(JunkFilter *junkfilter, TupleTableSlot *slot,
-					 char *attrName, Datum *value, bool *isNull);
+extern AttrNumber ExecFindJunkAttribute(JunkFilter *junkfilter,
+										const char *attrName);
+extern Datum ExecGetJunkAttribute(TupleTableSlot *slot, AttrNumber attno,
+								  bool *isNull);
 extern TupleTableSlot *ExecFilterJunk(JunkFilter *junkfilter,
 			   TupleTableSlot *slot);
 extern HeapTuple ExecRemoveJunk(JunkFilter *junkfilter, TupleTableSlot *slot);

src/include/nodes/execnodes.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/nodes/execnodes.h,v 1.161 2006/09/28 20:51:42 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/nodes/execnodes.h,v 1.162 2006/12/04 02:06:55 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -226,7 +226,8 @@ typedef struct ProjectionInfo
  *	  the tuple to be updated.	This is needed to do the update, but we
  *	  don't want the ctid to be part of the stored new tuple!  So, we
  *	  apply a "junk filter" to remove the junk attributes and form the
- *	  real output tuple.
+ *	  real output tuple.  The junkfilter code also provides routines to
+ *	  extract the values of the junk attribute(s) from the input tuple.
  *
  *	  targetList:		the original target list (including junk attributes).
  *	  cleanTupType:		the tuple descriptor for the "clean" tuple (with
@@ -235,6 +236,9 @@ typedef struct ProjectionInfo
  *						attribute numbers of the "original" tuple and the
  *						attribute numbers of the "clean" tuple.
  *	  resultSlot:		tuple slot used to hold cleaned tuple.
+ *	  junkAttNo:		not used by junkfilter code.  Can be used by caller
+ *						to remember the attno of a specific junk attribute
+ *						(execMain.c stores the "ctid" attno here).
  * ----------------
  */
 typedef struct JunkFilter
@@ -244,6 +248,7 @@ typedef struct JunkFilter
 	TupleDesc	jf_cleanTupType;
 	AttrNumber *jf_cleanMap;
 	TupleTableSlot *jf_resultSlot;
+	AttrNumber	jf_junkAttNo;
 } JunkFilter;
 
 /* ----------------
@@ -352,7 +357,7 @@ typedef struct ExecRowMark
 	Index		rti;			/* its range table index */
 	bool		forUpdate;		/* true = FOR UPDATE, false = FOR SHARE */
 	bool		noWait;			/* NOWAIT option */
-	char		resname[32];	/* name for its ctid junk attribute */
+	AttrNumber	ctidAttNo;		/* resno of its ctid junk attribute */
 } ExecRowMark;