Re: AIO v2.5

Hi,

On 2025-03-27 10:52:10 +1300, Thomas Munro wrote:
> On Thu, Mar 27, 2025 at 10:41 AM Andres Freund <andres(at)anarazel(dot)de> wrote:
> > > > Subject: [PATCH v2.12 13/28] Enable IO concurrency on all systems
> > >
> > > Consider also updating this comment to stop focusing on prefetch; I think
> > > changing that aligns with the patch's other changes:
> > >
> > > /*
> > > * How many buffers PrefetchBuffer callers should try to stay ahead of their
> > > * ReadBuffer calls by. Zero means "never prefetch". This value is only used
> > > * for buffers not belonging to tablespaces that have their
> > > * effective_io_concurrency parameter set.
> > > */
> > > int effective_io_concurrency = DEFAULT_EFFECTIVE_IO_CONCURRENCY;
> >
> > Good point. Although I suspect it might be worth adjusting this, and also the
> > config.sgml bit about effective_io_concurrency separately. That seems like it
> > might take an iteration or two.
>
> +1 for rewriting that separately from this work on the code (I can
> have a crack at that if you want).

You taking a crack at that would be appreciated!

> For the comment, my suggestion would be something like:
>
> "Default limit on the level of concurrency that each I/O stream
> (currently, ReadStream but in future other kinds of streams) can use.
> Zero means that I/O is always performed synchronously, ie not
> concurrently with query execution. This value can be overridden at the
> tablespace level with the parameter of the same name. Note that
> streams performing I/O not classified as single-session work respect
> maintenance_io_concurrency instead."

Generally sounds good. I do wonder if the last sentence could be made a bit
simpler, it took me a few seconds to parse "not classified as single-session".

Maybe "classified as performing work for multiple sessions respect
maintenance_io_concurrency instead."?

Greetings,

Andres Freund