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.
Greetings,
Andres Freund
