Date: Tue, 25 Mar 2025 13:18:50 -0700
From: Noah Misch <noah@leadboat.com>
To: Andres Freund <andres@anarazel.de>
Cc: Thomas Munro <thomas.munro@gmail.com>, Antonin Houska <ah@cybertec.at>,
	pgsql-hackers@postgresql.org, Heikki Linnakangas <hlinnaka@iki.fi>,
	Robert Haas <robertmhaas@gmail.com>,
	Jakub Wartak <jakub.wartak@enterprisedb.com>,
	Jelte Fennema-Nio <postgres@jeltef.nl>
Subject: Re: AIO v2.5
Message-ID: <20250325201850.55.nmisch@google.com>
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On Tue, Mar 25, 2025 at 04:07:35PM -0400, Andres Freund wrote:
> On 2025-03-25 12:39:56 -0700, Noah Misch wrote:
> > On Tue, Mar 25, 2025 at 02:58:37PM -0400, Andres Freund wrote:
> > > There are 2 1/2 ways around this:
> > > 
> > > 1) Stop using IOSQE_ASYNC heuristic
> > > 2a) Wait for all in-flight IOs when any FD gets closed
> > > 2b) Wait for all in-flight IOs using FD when it gets closed
> > > 
> > > Given that we have clear evidence that io_uring doesn't completely support
> > > closing FDs while IOs are in flight, be it a bug or intentional, it seems
> > > clearly better to go for 2a or 2b.
> > 
> > Agreed.  If a workload spends significant time on fd.c closing files, I
> > suspect that workload already won't have impressive benchmark numbers.
> > Performance-seeking workloads will already want to tune FD usage high enough
> > to keep FDs long-lived.  So (1) clearly loses, and neither (2a) nor (2b)
> > clearly beats the other.  I'd try (2b) first but, if complicated, quickly
> > abandon it in favor of (2a).  What other considerations could be important?
> 
> The only other consideration I can think of is whether this should happen for
> all io_methods or not.

Either way is fine, I think.

> I'm inclined to do it via a bool in IoMethodOps, but I guess one could argue
> it's a bit weird to have a bool in a struct called *Ops.

That wouldn't bother me.  IndexAmRoutine has many bools, and "Ops" is
basically a synonym of "Routine".