Re: Comments on Custom RMGRs

On Fri, Mar 22, 2024 at 2:02 AM Jeff Davis <pgsql(at)j-davis(dot)com> wrote:
> On Thu, 2024-03-21 at 19:47 +0700, Danil Anisimow wrote:
> > [pgss_001.v1.patch] adds a custom resource manager to the
> > pg_stat_statements extension.
>
> Did you consider moving the logic for loading the initial contents from
> disk from pgss_shmem_startup to .rmgr_startup?

I tried it, but .rmgr_startup is not called if the system was shut down
cleanly.

> My biggest concern is that it might not be quite right for a table AM
> that has complex state that needs action to be taken at a slightly
> different time, e.g. right after CheckPointBuffers().

> Then again, the rmgr is a low-level API, and any extension using it
> should be prepared to adapt to changes. If it works for pgss, then we
> know it works for at least one thing, and we can always improve it
> later. For instance, we might call the hook several times and pass it a
> "phase" argument.

In [rmgr_003.v3.patch] I added a phase argument to RmgrCheckpoint().
Currently it is only called in two places: before and after
CheckPointBuffers().

--
Regards,
Daniil Anisimov
Postgres Professional: http://postgrespro.com