Feedback-ID: id4a34324:Fastmail
Date: Mon, 10 Feb 2025 18:30:56 -0500
From: Andres Freund <andres@anarazel.de>
To: Jelte Fennema-Nio <postgres@jeltef.nl>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, torikoshia <torikoshia@oss.nttdata.com>, 
	pgsql-hackers@postgresql.org, rjuju123@gmail.com, Bruce Momjian <bruce@momjian.us>
Subject: Re: RFC: Allow EXPLAIN to Output Page Fault Information
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Hi,

On 2025-02-10 23:52:17 +0100, Jelte Fennema-Nio wrote:
> On Mon, 10 Feb 2025 at 14:31, Andres Freund <andres@anarazel.de> wrote:
> > But this will also not work with AIO w/ Buffered IO. Which we hope to use much
> > more commonly.
> 
> To be clear, here you mean worker based AIO right? Because it would
> work with io_uring based AIO, right?

I mostly meant worker based AIO, yes. I haven't checked how accurately these
are kept for io_uring. I would hope they are...


> > If suddenly I have to reimplement something like this to work with worker
> > based IO, it'll certainly take longer to get to AIO.
> 
> I totally understand. But in my opinion it would be completely fine to
> decide that these new IO stats are simply not available for worker
> based IO. Just like they're not available for Windows either with this
> patch.

The thing is that you'd often get completely misleading stats. Some of the IO
will still be done by the backend itself, so there will be a non-zero
value. But it will be a significant undercount, because the asynchronously
executed IO won't be tracked (if worker mode is used).

Greetings,

Andres Freund