Improve coding pattern in Parallel Append code.

Amit Kapila · Amit Kapila · commit 98d476a965ee · 2018-06-22T08:43:36.000+05:30
The create_append_path code didn't consider that list_concat will modify it's first argument leading to inconsistent traversal of resulting list. In practice, it won't lead to any user-visible bug but changing it for making the code behave consistently. Reported-by: Tom Lane Author: Tom Lane Reviewed-by: Amit Khandekar and Amit Kapila Discussion: https://postgr.es/m/32365.1528994120@sss.pgh.pa.us
diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c
@@ -1274,7 +1274,7 @@ create_append_path(PlannerInfo *root,
 	pathnode->first_partial_path = list_length(subpaths);
 	pathnode->subpaths = list_concat(subpaths, partial_subpaths);
 
-	foreach(l, subpaths)
+	foreach(l, pathnode->subpaths)
 	{
 		Path	   *subpath = (Path *) lfirst(l);
 

Original file line number	Diff line number	Diff line change
`@@ -1274,7 +1274,7 @@ create_append_path(PlannerInfo *root,`
`1274`	`1274`	`pathnode->first_partial_path = list_length(subpaths);`
`1275`	`1275`	`pathnode->subpaths = list_concat(subpaths, partial_subpaths);`
`1276`	`1276`
`1277`		`- foreach(l, subpaths)`
	`1277`	`+ foreach(l, pathnode->subpaths)`
`1278`	`1278`	`{`
`1279`	`1279`	`Path subpath = (Path ) lfirst(l);`
`1280`	`1280`