From: | Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com> |
---|---|
To: | PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
Subject: | minor bug in sort_inner_and_outer() |
Date: | 2022-01-14 00:48:33 |
Message-ID: | bf3a6ea1-a7d8-7211-0669-189d5c169374@enterprisedb.com |
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Lists: | pgsql-hackers |
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
Attachment | Content-Type | Size |
---|---|---|
sort-inner-and-outer-fix.patch | text/x-patch | 492 bytes |
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