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Tue, 24 Feb 2026 10:16:19 +0100 From: Attila Soki Message-Id: <1C445A2F-3256-4F04-B55D-9850581FF39A@gmx.net> Content-Type: multipart/alternative; boundary="Apple-Mail=_345A2F21-43E5-4B53-AE23-5BDDA2A7E0DA" Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3864.400.21\)) Subject: Re: unstable query plan on pg 16,17,18 Date: Tue, 24 Feb 2026 10:16:08 +0100 In-Reply-To: <5bace3e5-3d6b-4f81-92a9-9ff4e9e5de53@gmail.com> Cc: pgsql-performance@postgresql.org To: Andrei Lepikhov References: <64ddfe83-317c-4cf1-b04f-cb74d9f40629@gmail.com> <529E2365-6C3F-4BDA-9625-312F3A023C5B@gmx.net> <5bace3e5-3d6b-4f81-92a9-9ff4e9e5de53@gmail.com> X-Mailer: Apple Mail (2.3864.400.21) X-Provags-ID: V03:K1:svb/ceDzOEnn0gKZouG7JxUT0F6fCQYmg69GpHy7BlPTMQxsf/z 2nETs9TDw/2yL3AOZ2tYpEOJQlNwJmJpJx62f4nMfsHhY8C/SFPNhiN536nQzkZOqmRwvqU RJ5bBC6/tuFTA7aN5ToJ6PTJhheIYsoZJZcet41yomrib5/TKGBNtMA/uKswWEv0QXEFsU8 Og+zXOu75RNSEZJ6hWw1w== X-Spam-Flag: NO UI-OutboundReport: notjunk:1;M01:P0:VHuHHzOOZc4=;KNfPe5VBQxHw8i5ya3zk0gFHKFQ 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Lepikhov wrote: > Thanks. But I meant your 'good' plan built by the PG14. I think a new = feature invented later has added some problems. >=20 > Current conjecture is the following. As I see, the main problem is = with Right Hash Join: > -> Hash Right Join (cost=3D210369.25..210370.30 rows=3D8 width=3D99) > Its inner side (Hash table) is rebuilt multiple times (around 1k) due = to an external parameter (gauf_1.id) in the subtree. It looks like a = disaster, and before I thought we don't build hash tables over = parameterised query trees at all. >=20 > So, let me discover a little more, but your PG14 explain could add = more details here. Sorry, I misunderstood that. here is the pg14.4 explain https://explain.depesz.com/s/eb32 Regards, Attila= --Apple-Mail=_345A2F21-43E5-4B53-AE23-5BDDA2A7E0DA Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=us-ascii On 23 Feb 2026, at 21:25, Andrei = Lepikhov <lepihov@gmail.com> wrote:
Thanks. But I meant your 'good' plan built by the PG14. I = think a new feature invented later has added some = problems.

Current conjecture is the following. As I = see, the main problem is with Right Hash Join:
-> Hash Right Join = (cost=3D210369.25..210370.30 rows=3D8 width=3D99)
Its inner side = (Hash table) is rebuilt multiple times (around 1k) due to an external = parameter (gauf_1.id) in the subtree. It looks like a disaster, and = before I thought we don't build hash tables over parameterised query = trees at all.

So, let me discover a little more, but your PG14 = explain could add more details = here.

Sorry, I misunderstood = that.
here is the pg14.4 explain


Regards,
Attila
= --Apple-Mail=_345A2F21-43E5-4B53-AE23-5BDDA2A7E0DA--