minor bug in sort_inner_and_outer()
Hi,
While looking at sort_inner_and_outer() I was rather confused what is
stored in all_pathkeys, because the code does this:
List *all_pathkeys;
...
all_pathkeys = select_outer_pathkeys_for_merge(root,
extra->mergeclause_list,
joinrel);
foreach(l, all_pathkeys)
{
List *front_pathkey = (List *) lfirst(l);
...
/* Make a pathkey list with this guy first */
if (l != list_head(all_pathkeys))
outerkeys = lcons(front_pathkey,
...);
else
...
which seems to suggest all_pathkeys is a list of lists, because why else
would front_pathkey be a (List *). But that doesn't seem to be the case,
front_pathkey is actually a PathKey, not a List, as demonstrated by gdb:
(gdb) p *front_pathkey
$2 = {type = T_PathKey, length = 0, ...}
Maybe it's some clever list-fu that I can't comprehend, but I guess it's
a bug present since ~2004. It's benign because we only ever pass the
front_pathkey to lcons() which does not really care.
regards
--
Tomas Vondra
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
Attachments:
sort-inner-and-outer-fix.patchtext/x-patch; charset=UTF-8; name=sort-inner-and-outer-fix.patchDownload
diff --git a/src/backend/optimizer/path/joinpath.c b/src/backend/optimizer/path/joinpath.c
index f96fc9fd282..81e04b6ac9d 100644
--- a/src/backend/optimizer/path/joinpath.c
+++ b/src/backend/optimizer/path/joinpath.c
@@ -1258,7 +1258,7 @@ sort_inner_and_outer(PlannerInfo *root,
foreach(l, all_pathkeys)
{
- List *front_pathkey = (List *) lfirst(l);
+ PathKey *front_pathkey = lfirst_node(PathKey, l);
List *cur_mergeclauses;
List *outerkeys;
List *innerkeys;