Re: AIO v2.5

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). 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."