Hi, On Thu, Oct 31, 2024 at 05:09:56AM +0000, Bertrand Drouvot wrote: > === OPTIONS === > > So, based on this, I think that we could: > > Option 1: "move" the existing PGSTAT_KIND_IO to variable-numbered and let this > KIND take care of the aggregated view (pg_stat_io) and the per-backend stats. > > Option 2: let PGSTAT_KIND_IO as it is and introduce a new > PGSTAT_KIND_BACKEND_IO > that would be variable-numbered. > > Option 3: Remove PGSTAT_KIND_IO, introduce a new PGSTAT_KIND_BACKEND_IO that > would be variable-numbered and store the "aggregated stats aka pg_stat_io" in > shared memory (not part of the variable-numbered hash). Per-backend stats > could be aggregated into "pg_stat_io" during the flush_pending_cb call for > example. > > === BEST OPTION? === > > I would opt for Option 2 as: > > - The stats system is currently not designed for Option 1 and our goals (for > example the shared_data_len is used to serialize but also to fetch the > entries, > see pgstat_fetch_entry()) so that would need some hack to serialize only a > part > of them and still be able to fetch them all). > > - Mixing "fixed" and "variable" in the same KIND does not sound like a good > idea > (though that might be possible with some hacks, I don't think that would be > easy to maintain). > > - Having the per-backend as "variable" in its dedicated kind looks more > reasonable > and less error-prone. > > - I don't think there is a stats design similar to option 3 currently, so I'm > not sure there is a need to develop something new while Option 2 could be > done. > > - Option 3 would need some hack for (at least) the "pg_stat_io" > [de]serialization > part. > > - Option 2 seems to offer more flexibility (as compare to Option 1 and 3). > > Thoughts?
And why not add more per-backend stats in the future? (once the I/O part is done). I think that's one more reason to go with option 2 (and implementing a brand new PGSTAT_KIND_BACKEND kind). Thoughts? Regards, -- Bertrand Drouvot PostgreSQL Contributors Team RDS Open Source Databases Amazon Web Services: https://aws.amazon.com
