Optimize a few list_delete_ptr calls

david-rowley · david-rowley · commit e7c2b95d37a2 · 2020-10-22T14:36:32.000+13:00
There is a handful of places where we called list_delete_ptr() to remove some element from a List. In many of these places we know, or with very little additional effort know the index of the ListCell that we need to remove. Here we change all of those places to instead either use one of; list_delete_nth_cell(), foreach_delete_current() or list_delete_last(). Each of these saves from having to iterate over the list to search for the element to remove by its pointer value. There are some small performance gains to be had by doing this, but in the general case, none of these lists are likely to be very large, so the lookup was probably never that expensive anyway. However, some of the calls are in fairly hot code paths, e.g process_equivalence(). So any small gains there are useful. Author: Zhijie Hou and David Rowley Discussion: https://postgr.es/m/b3517353ec7c4f87aa560678fbb1034b@G08CNEXMBPEKD05.g08.fujitsu.local
diff --git a/src/backend/optimizer/path/equivclass.c b/src/backend/optimizer/path/equivclass.c
@@ -137,6 +137,7 @@ process_equivalence(PlannerInfo *root,
 	EquivalenceMember *em1,
 			   *em2;
 	ListCell   *lc1;
+	int			ec2_idx;
 
 	/* Should not already be marked as having generated an eclass */
 	Assert(restrictinfo->left_ec == NULL);
@@ -258,6 +259,7 @@ process_equivalence(PlannerInfo *root,
 	 */
 	ec1 = ec2 = NULL;
 	em1 = em2 = NULL;
+	ec2_idx = -1;
 	foreach(lc1, root->eq_classes)
 	{
 		EquivalenceClass *cur_ec = (EquivalenceClass *) lfirst(lc1);
@@ -311,6 +313,7 @@ process_equivalence(PlannerInfo *root,
 				equal(item2, cur_em->em_expr))
 			{
 				ec2 = cur_ec;
+				ec2_idx = foreach_current_index(lc1);
 				em2 = cur_em;
 				if (ec1)
 					break;
@@ -371,7 +374,7 @@ process_equivalence(PlannerInfo *root,
 		ec1->ec_max_security = Max(ec1->ec_max_security,
 								   ec2->ec_max_security);
 		ec2->ec_merged = ec1;
-		root->eq_classes = list_delete_ptr(root->eq_classes, ec2);
+		root->eq_classes = list_delete_nth_cell(root->eq_classes, ec2_idx);
 		/* just to avoid debugging confusion w/ dangling pointers: */
 		ec2->ec_members = NIL;
 		ec2->ec_sources = NIL;
@@ -1964,6 +1967,7 @@ reconsider_full_join_clause(PlannerInfo *root, RestrictInfo *rinfo)
 		bool		matchleft;
 		bool		matchright;
 		ListCell   *lc2;
+		int			coal_idx = -1;
 
 		/* Ignore EC unless it contains pseudoconstants */
 		if (!cur_ec->ec_has_const)
@@ -2008,6 +2012,7 @@ reconsider_full_join_clause(PlannerInfo *root, RestrictInfo *rinfo)
 
 				if (equal(leftvar, cfirst) && equal(rightvar, csecond))
 				{
+					coal_idx = foreach_current_index(lc2);
 					match = true;
 					break;
 				}
@@ -2072,7 +2077,7 @@ reconsider_full_join_clause(PlannerInfo *root, RestrictInfo *rinfo)
 		 */
 		if (matchleft && matchright)
 		{
-			cur_ec->ec_members = list_delete_ptr(cur_ec->ec_members, coal_em);
+			cur_ec->ec_members = list_delete_nth_cell(cur_ec->ec_members, coal_idx);
 			return true;
 		}
 
diff --git a/src/backend/optimizer/path/joinpath.c b/src/backend/optimizer/path/joinpath.c
@@ -1005,8 +1005,8 @@ sort_inner_and_outer(PlannerInfo *root,
 		/* Make a pathkey list with this guy first */
 		if (l != list_head(all_pathkeys))
 			outerkeys = lcons(front_pathkey,
-							  list_delete_ptr(list_copy(all_pathkeys),
-											  front_pathkey));
+							  list_delete_nth_cell(list_copy(all_pathkeys),
+												   foreach_current_index(l)));
 		else
 			outerkeys = all_pathkeys;	/* no work at first one... */
 
diff --git a/src/backend/parser/parse_expr.c b/src/backend/parser/parse_expr.c
@@ -1698,11 +1698,12 @@ transformMultiAssignRef(ParseState *pstate, MultiAssignRef *maref)
 		/*
 		 * If we're at the last column, delete the RowExpr from
 		 * p_multiassign_exprs; we don't need it anymore, and don't want it in
-		 * the finished UPDATE tlist.
+		 * the finished UPDATE tlist.  We assume this is still the last entry
+		 * in p_multiassign_exprs.
 		 */
 		if (maref->colno == maref->ncolumns)
 			pstate->p_multiassign_exprs =
-				list_delete_ptr(pstate->p_multiassign_exprs, tle);
+				list_delete_last(pstate->p_multiassign_exprs);
 
 		return result;
 	}
diff --git a/src/backend/parser/parse_utilcmd.c b/src/backend/parser/parse_utilcmd.c
@@ -360,6 +360,7 @@ generateSerialExtraStmts(CreateStmtContext *cxt, ColumnDef *column,
 	CreateSeqStmt *seqstmt;
 	AlterSeqStmt *altseqstmt;
 	List	   *attnamelist;
+	int			nameEl_idx = -1;
 
 	/*
 	 * Determine namespace and name to use for the sequence.
@@ -386,6 +387,7 @@ generateSerialExtraStmts(CreateStmtContext *cxt, ColumnDef *column,
 						(errcode(ERRCODE_SYNTAX_ERROR),
 						 errmsg("conflicting or redundant options")));
 			nameEl = defel;
+			nameEl_idx = foreach_current_index(option);
 		}
 	}
 
@@ -405,7 +407,7 @@ generateSerialExtraStmts(CreateStmtContext *cxt, ColumnDef *column,
 		}
 		sname = rv->relname;
 		/* Remove the SEQUENCE NAME item from seqoptions */
-		seqoptions = list_delete_ptr(seqoptions, nameEl);
+		seqoptions = list_delete_nth_cell(seqoptions, nameEl_idx);
 	}
 	else
 	{
diff --git a/src/backend/rewrite/rewriteHandler.c b/src/backend/rewrite/rewriteHandler.c
@@ -650,11 +650,7 @@ adjustJoinTreeList(Query *parsetree, bool removert, int rt_index)
 			if (IsA(rtr, RangeTblRef) &&
 				rtr->rtindex == rt_index)
 			{
-				newjointree = list_delete_ptr(newjointree, rtr);
-
-				/*
-				 * foreach is safe because we exit loop after list_delete...
-				 */
+				newjointree = foreach_delete_current(newjointree, l);
 				break;
 			}
 		}

Original file line number	Diff line number	Diff line change
`@@ -360,6 +360,7 @@ generateSerialExtraStmts(CreateStmtContext cxt, ColumnDef column,`
`360`	`360`	`CreateSeqStmt *seqstmt;`
`361`	`361`	`AlterSeqStmt *altseqstmt;`
`362`	`362`	`List *attnamelist;`
	`363`	`+ int nameEl_idx = -1;`
`363`	`364`
`364`	`365`	`/*`
`365`	`366`	`* Determine namespace and name to use for the sequence.`
`@@ -386,6 +387,7 @@ generateSerialExtraStmts(CreateStmtContext cxt, ColumnDef column,`
`386`	`387`	`(errcode(ERRCODE_SYNTAX_ERROR),`
`387`	`388`	`errmsg("conflicting or redundant options")));`
`388`	`389`	`nameEl = defel;`
	`390`	`+ nameEl_idx = foreach_current_index(option);`
`389`	`391`	`}`
`390`	`392`	`}`
`391`	`393`
`@@ -405,7 +407,7 @@ generateSerialExtraStmts(CreateStmtContext cxt, ColumnDef column,`
`405`	`407`	`}`
`406`	`408`	`sname = rv->relname;`
`407`	`409`	`/* Remove the SEQUENCE NAME item from seqoptions */`
`408`		`- seqoptions = list_delete_ptr(seqoptions, nameEl);`
	`410`	`+ seqoptions = list_delete_nth_cell(seqoptions, nameEl_idx);`
`409`	`411`	`}`
`410`	`412`	`else`
`411`	`413`	`{`
Original file line number	Diff line number	Diff line change
`@@ -650,11 +650,7 @@ adjustJoinTreeList(Query *parsetree, bool removert, int rt_index)`
`650`	`650`	`if (IsA(rtr, RangeTblRef) &&`
`651`	`651`	`rtr->rtindex == rt_index)`
`652`	`652`	`{`
`653`		`- newjointree = list_delete_ptr(newjointree, rtr);`
`654`		`-`
`655`		`- /*`
`656`		`- * foreach is safe because we exit loop after list_delete...`
`657`		`- */`
	`653`	`+ newjointree = foreach_delete_current(newjointree, l);`
`658`	`654`	`break;`
`659`	`655`	`}`
`660`	`656`	`}`