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help / color / mirror / Atom feedFrom: Xuneng Zhou <[email protected]>
To: Andres Freund <[email protected]>
Cc: Michael Paquier <[email protected]>
Cc: pgsql-hackers <[email protected]>
Cc: Nazir Bilal Yavuz <[email protected]>
Subject: Re: Streamify more code paths
Date: Wed, 11 Mar 2026 10:23:36 +0800
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Hi,
On Wed, Mar 11, 2026 at 8:16 AM Andres Freund <[email protected]> wrote:
>
> Hi,
>
> On 2026-03-10 19:27:59 -0400, Andres Freund wrote:
> > > > pgstattuple_large base= 12429.3ms patch= 11916.8ms 1.04x
> > > > ( 4.1%) (reads=206945->12983, io_time=6501.91->32.24ms)
> > >
> > > > pgstattuple_large base= 12642.9ms patch= 11873.5ms 1.06x
> > > > ( 6.1%) (reads=206945->12983, io_time=6516.70->143.46ms)
> > >
> > > Yeah, this looks somewhat strange. The io_time has been reduced
> > > significantly, which should also lead to a substantial reduction in
> > > runtime.
> >
> > It's possible that the bottleneck just moved, e.g to the checksum computation,
> > if you have data checksums enabled.
> >
> > It's also worth noting that likely each of the test reps measures
> > something different, as likely
> > psql_run "$ROOT" "$PORT" -c "UPDATE heap_test SET data = data || '!' WHERE id % 5 = 0;"
> >
> > leads to some out-of-page updates.
> >
> > You're probably better off deleting some of the data in a transaction that is
> > then rolled back. That will also unset all-visible, but won't otherwise change
> > the layout, no matter how many test iterations you run.
> >
> >
> > I'd also guess that you're seeing a relatively small win because you're
> > updating every page. When reading every page from disk, the OS can do
> > efficient readahead. If there are only occasional misses, that does not work.
>
> I think that last one is a big part - if I use
> BEGIN; DELETE FROM heap_test WHERE id % 500 = 0; ROLLBACK;
> (which leaves a lot of
>
> I see much bigger wins due to the pgstattuple changes.
>
> time buffered time DIO
> w/o read stream 2222.078 ms 2090.239 ms
> w read stream 299.455 ms 155.124 ms
>
> That's with local storage. io_uring, but numbers with worker are similar.
>
The results look great and interesting. This looks far better than
what I observed in my earlier tests. I’ll run perf for pgstattuple
without the switching to see what is keeping the CPU busy.
--
Best,
Xuneng
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