Re: Support to define custom wait events for extensions

Hi,

On 2023-08-01 12:14:49 +0900, Michael Paquier wrote:
> On Tue, Aug 01, 2023 at 11:51:35AM +0900, Masahiro Ikeda wrote:
> > Thanks for committing the main patch.
> >
> > In my understanding, the rest works are
> > * to support WaitEventExtensionMultiple()
> > * to replace WAIT_EVENT_EXTENSION to custom wait events
> >
> > Do someone already works for them? If not, I'll consider
> > how to realize them.
>
> Note that postgres_fdw and dblink use WAIT_EVENT_EXTENSION, but have
> no dependency to shared_preload_libraries. Perhaps these could just
> use a dynamic handling but that deserves a separate discussion because
> of the fact that they'd need shared memory without being able to
> request it. autoprewarm.c is much simpler.

This is why the scheme as implemented doesn't really make sense to me. It'd be
much easier to use if we had a shared hashtable with the identifiers than
what's been merged now.

In plenty of cases it's not realistic for an extension library to run in each
backend, while still needing to wait for things.

Greetings,

Andres Freund