Feedback-ID: id4a34324:Fastmail
Date: Thu, 21 Dec 2023 07:43:52 -0800
From: Andres Freund <andres@anarazel.de>
To: Tomas Vondra <tomas.vondra@enterprisedb.com>
Cc: Robert Haas <robertmhaas@gmail.com>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
	Georgios <gkokolatos@protonmail.com>
Subject: Re: index prefetching
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Hi,

On 2023-12-21 16:20:45 +0100, Tomas Vondra wrote:
> On 12/21/23 14:43, Andres Freund wrote:
> >> AFAICS this seems similar to some of the AIO patch, I wonder what that
> >> plans to do. I need to check.
> > 
> > Yes, most of this exists there.  The difference that with the AIO you don't
> > need to prefetch, as you can just initiate the IO for real, and wait for it to
> > complete.
> > 
> 
> Right, although the line where things stop being "prefetch" and becomes
> "async" seems a bit unclear to me / perhaps more a point of view.

Agreed. What I meant with not needing prefetching was that you'd not use
fadvise(), because it's better to instead just asynchronously read data into
shared buffers. That way you don't have the doubling of syscalls and you don't
need to care less about the buffering rate in the kernel.

Greetings,

Andres Freund