Re: Comments on Custom RMGRs

On Fri, Mar 1, 2024 at 2:06 AM Jeff Davis <pgsql(at)j-davis(dot)com> wrote:
> Added to March CF.
>
> I don't have an immediate use case in mind for this, so please drive
> that part of the discussion. I can't promise this for 17, but if the
> patch is simple enough and a quick consensus develops, then it's
> possible.

[pgss_001.v1.patch] adds a custom resource manager to the
pg_stat_statements extension. The proposed patch is not a complete solution
for pgss and may not work correctly with replication.

The 020_crash.pl test demonstrates server interruption by killing a
backend. Without rm_checkpoint hook, the server restores pgss stats only
after last CHECKPOINT. Data added to WAL before the checkpoint is not
restored.

The rm_checkpoint hook allows saving shared memory data to disk at each
checkpoint. However, for pg_stat_statements, it matters when the checkpoint
occurred. When the server shuts down, pgss deletes the temporary file of
query texts. In other cases, this is unacceptable.
To provide this capability, a flags parameter was added to the
rm_checkpoint hook. The changes are presented in [rmgr_003.v2.patch].

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