Re: relfilenode statistics

On Wed, Jun 5, 2024 at 1:52 AM Bertrand Drouvot
<bertranddrouvot.pg@gmail.com> wrote:
> I think we should keep the stats in the relation during relfilenode changes.
> As a POC, v1 implemented a way to do so during TRUNCATE (see the changes in
> table_relation_set_new_filelocator() and in pg_statio_all_tables): as you can
> see in the example provided up-thread the new heap_blks_written statistic has
> been preserved during the TRUNCATE.

Yeah, I think there's something weird about this design. Somehow we're
ending up with both per-relation and per-relfilenode counters:

+                       pg_stat_get_blocks_written(C.oid) +
pg_stat_get_relfilenode_blocks_written(d.oid, CASE WHEN
C.reltablespace <> 0 THEN C.reltablespace ELSE d.dattablespace END,
C.relfilenode) AS heap_blks_written,

I'll defer to Andres if he thinks that's awesome, but to me it does
not seem right to track some blocks written in a per-relation counter
and others in a per-relfilenode counter.

--
Robert Haas
EDB: http://www.enterprisedb.com