| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Peter Geoghegan <pg(at)bowt(dot)ie> |
| Cc: | Tomas Vondra <tomas(at)vondra(dot)me>, Nikolay Samokhvalov <nik(at)postgres(dot)ai>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: EXPLAIN: showing ReadStream / prefetch stats |
| Date: | 2026-09-22 15:38:14 |
| Message-ID: | 462zvzr4m5a2q3xtfwz35ehpzgpan5pjcgul7wkmnouobujcbg@at3ezkpvwt4w |
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| Lists: | pgsql-hackers |
Hi,
On 2026-09-22 11:35:29 -0400, Peter Geoghegan wrote:
> On Tue, Sep 22, 2026 at 11:23 AM Tomas Vondra <tomas(at)vondra(dot)me> wrote:
> > In other words, I/O and buffers may disagree - that's not a bug. Those
> > counters are tracking different things.
+1
> > To handle this correctly, we'd need to find a way to not issue the I/O
> > at all (since 862092932c9479b79732f3b441da05453ea5e06d we discard I/O
> > that was not initiated yet).
>
> Isn't this what Andres' experimental "Make read_stream_reset()/end()
> not wait for IO" patch does? See:
>
> https://www.postgresql.org/message-id/f3xxfrkafjxpyqxywcxricxgyizjirfceychyxsgn7bwjp5eda@kwbduhy7tfmu
>
> This is one of the patches that I've been posting as part of the index
> prefetching patch series for some time now.
They're still issued in that patch, we just don't wait for them anymore. But I
think even so, they should still be accounted for.
Greetings,
Andres Freund
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