Date: Mon, 30 Sep 2024 12:29:53 -0700
From: Noah Misch <noah@leadboat.com>
To: Andres Freund <andres@anarazel.de>
Cc: pgsql-hackers@postgresql.org, Heikki Linnakangas <hlinnaka@iki.fi>,
	=?utf-8?B?6ZmI5a6X5b+X?= <baotiao@gmail.com>
Subject: Re: AIO v2.0
Message-ID: <20240930192953.19.nmisch@google.com>
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On Mon, Sep 30, 2024 at 10:49:17AM -0400, Andres Freund wrote:
> We also discussed the topic at https://postgr.es/m/20240925020022.c5.nmisch%40google.com
> > ... neither BM_SETTING_HINTS nor keeping bounce buffers looks like a bad
> > decision.  From what I've heard so far of the performance effects, if it were
> > me, I would keep the bounce buffers.  I'd pursue BM_SETTING_HINTS and bounce
> > buffer removal as a distinct project after the main AIO capability.  Bounce
> > buffers have an implementation.  They aren't harming other design decisions.
> > The AIO project is big, so I'd want to err on the side of not designating
> > other projects as its prerequisites.
> 
> Given the issues that modifying pages while in flight causes, not just with PG
> level checksums, but also filesystem level checksum, I don't feel like it's a
> particularly promising approach.
> 
> However, I think this doesn't have to mean that the BM_SETTING_HINTS stuff has
> to be completed before we can move forward with AIO. If I split out the write
> portion from the read portion a bit further, the main AIO changes and the
> shared-buffer read user can be merged before there's a dependency on the hint
> bit stuff being done.
> 
> Does that seem reasonable?

Yes.