|From:||Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>|
|To:||James Coleman <jtc331(at)gmail(dot)com>|
|Cc:||Jaime Casanova <jaime(dot)casanova(at)2ndquadrant(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>|
|Subject:||Re: enable_incremental_sort changes query behavior|
|Views:||Raw Message | Whole Thread | Download mbox | Resend email|
On Tue, Oct 06, 2020 at 09:37:31AM -0400, James Coleman wrote:
>On Tue, Oct 6, 2020 at 9:28 AM Jaime Casanova
>> Can you please create an entry in the commitfest for this one so we
>> don't lose track of it?
We're not too far from the next minor release, so I've been looking at
this fix again and I intend to get it committed shortly (on Monday or
so). Attached is a slightly modified version of the v4 patch that:
(a) Removes comments about projections added to code that is not
directly related to the fix. I'm not against adding such comments
(b) Fixes comment in expected output of incremental_sort test.
(c) Removes else branch from find_em_expr_usable_for_sorting_rel. It's
not quite needed thanks to the "return" in the "if" branch. IMO this
makes it more elegant.
I do have two questions about find_em_expr_usable_for_sorting_rel.
(a) Where does the em_is_const check come from? The comment claims we
should not be trying to sort by equivalence class members, but I can't
convince myself it's actually true and I don't see it discussed in this
(b) In find_em_expr_for_rel, which was what was used before, the
condition on relids was this:
if (bms_is_subset(em->em_relids, rel->relids) &&
but here we're using only
if (!bms_is_subset(em->em_relids, rel->relids))
Isn't this missing the second bms_is_empty condition?
Of course, an alternative to this fix would be reverting ba3e76cc571
(completely or just the part introducing generate_useful_gather_paths).
If anyone thinks that's what we should do, please speak now.
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
|Next Message||Daniel Gustafsson||2020-10-29 22:48:57||contrib/sslinfo cleanup and OpenSSL errorhandling|
|Previous Message||Victor Yegorov||2020-10-29 22:05:28||Re: Deleting older versions in unique indexes to avoid page splits|