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help / color / mirror / Atom feedFrom: Richard Guo <[email protected]>
To: Matheus Alcantara <[email protected]>
Cc: Robert Haas <[email protected]>
Cc: Tom Lane <[email protected]>
Cc: Tender Wang <[email protected]>
Cc: Paul George <[email protected]>
Cc: Andy Fan <[email protected]>
Cc: PostgreSQL-development <[email protected]>
Cc: [email protected]
Subject: Re: Eager aggregation, take 3
Date: Thu, 2 Oct 2025 10:39:50 +0900
Message-ID: <CAMbWs48V+1d3zQPfpgpKEGWzMi7gBnkJtJq94-Tuf69-9YRh1w@mail.gmail.com> (raw)
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On Thu, Oct 2, 2025 at 10:13 AM Richard Guo <[email protected]> wrote:
> On Thu, Oct 2, 2025 at 8:55 AM Matheus Alcantara
> <[email protected]> wrote:
> > The query 31 seems bad, I don't know if I'm doing something completely
> > wrong but I've just setup a TPC-DS database and then executed the query
> > on master and with the v23 patch and I got these results:
> >
> > Master:
> > Planning Time: 3.191 ms
> > Execution Time: 16950.619 ms
> >
> > Patch:
> > Planning Time: 3.257 ms
> > Execution Time: 3848355.646 ms
> Thanks for reporting this. It does seem odd. I checked the TPC-DS
> benchmarking on v13 and found that the execution time for query 31,
> with and without eager aggregation, is as follows:
>
> EAGER-AGG-OFF EAGER-AGG-ON
> q31 10463.536 ms 10244.175 ms
>
> There appears to be a regression between v13 and v23. Looking into
> it...
I noticed something interesting while comparing the two EXPLAIN
(ANALYZE) outputs: the patched version uses parallel plans, whereas
the master does not. To rule that out as a factor, I ran "SET
max_parallel_workers_per_gather TO 0;" and re-ran query 31 on both
master and the patched version. This time, I got a positive result.
-- on master
Planning Time: 5.281 ms
Execution Time: 7222.665 ms
-- on patched
Planning Time: 4.855 ms
Execution Time: 5977.287 ms
It seems eager aggregation doesn't cope well with parallel plans for
this query. Looking into it.
- Richard
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Subject: Re: Eager aggregation, take 3
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