public inbox for [email protected]  

help / color / mirror / Atom feed

From: Melanie Plageman <[email protected]>
To: Andres Freund <[email protected]>
Cc: Nazir Bilal Yavuz <[email protected]>
Cc: [email protected]
Cc: Thomas Munro <[email protected]>
Cc: Peter Geoghegan <[email protected]>
Cc: Tomas Vondra <[email protected]>
Subject: Re: AIO / read stream heuristics adjustments for index prefetching
Date: Fri, 3 Apr 2026 12:45:50 -0400
Message-ID: <CAAKRu_bWPO-w3arE3pM5i5LArp7mA+Rg0chm-1WL-JxvDxv7Cg@mail.gmail.com> (raw)
In-Reply-To: <aafskrrvefnb6p7zg3xnzau3m2iywfwrxfcmqx5vr7673j4qio@hha6e55rolqd>
References: <f3xxfrkafjxpyqxywcxricxgyizjirfceychyxsgn7bwjp5eda@kwbduhy7tfmu>
	<CAAKRu_ZcJnnxgDQaXjuhd37bnc-jKARBU4EDi+LUqgs+ZjmrgQ@mail.gmail.com>
	<b7cxivohlk7hfl6qcqxbutrpoukunawxvarr2g2o6jicwkyx5o@qtzdj36ihyz5>
	<CAN55FZ3GT+o545U9JLR0AC5JtBznqJP4Mf9Mi4k3axqqAXTxPg@mail.gmail.com>
	<aafskrrvefnb6p7zg3xnzau3m2iywfwrxfcmqx5vr7673j4qio@hha6e55rolqd>

On Thu, Apr 2, 2026 at 9:33 AM Andres Freund <[email protected]> wrote:
>
> > +                /*
> > +                 * XXX: Should we actually reduce this at any time other than
> > +                 * a reset? For now we have to, as this is also a condition
> > +                 * for re-enabling fast_path.
> > +                 */
> > +                if (stream->combine_distance > 1)
> > +                    stream->combine_distance--;
> >
> > I don't think we need to reduce this other than reset.
>
> Hm. I go back and forth on that one :)

Separate from the fast-path enablement, we also probably want to
decrease combine distance when we decrease readahead_distance because
there is a point where we still want to parallelize the IOs even when
the distance is lower and to do that, we need to make smaller IOs. I'm
not sure where this point is, but I wonder if a few 256kB IOs is
faster than 1 1MB IO (could test that with fio actually). I imagine
that there is some size where that is true because of peculiarities in
how drives (and cloud storage) issue/break up IOs after they are a
certain size, etc.

- Melanie

view thread (23+ messages)  latest in thread

reply

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Reply to all the recipients using the --to and --cc options:
  reply via email

  To: [email protected]
  Cc: [email protected], [email protected], [email protected], [email protected], [email protected], [email protected]
  Subject: Re: AIO / read stream heuristics adjustments for index prefetching
  In-Reply-To: <CAAKRu_bWPO-w3arE3pM5i5LArp7mA+Rg0chm-1WL-JxvDxv7Cg@mail.gmail.com>

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

This inbox is served by agora; see mirroring instructions
for how to clone and mirror all data and code used for this inbox