On Sun, Apr 23, 2023 at 12:55 AM Jonathan S. Katz <jk...@postgresql.org> wrote: > > On 4/19/23 1:23 PM, Andres Freund wrote: > > Hi, > > > > I noticed that the numbers in pg_stat_io dont't quite add up to what I > > expected in write heavy workloads. Particularly for checkpointer, the > > numbers > > for "write" in log_checkpoints output are larger than what is visible in > > pg_stat_io. > > > > That partially is because log_checkpoints' "write" covers way too many > > things, > > but there's an issue with pg_stat_io as well: > > > > Checkpoints, and some other sources of writes, will often end up doing a lot > > of smgrwriteback() calls - which pg_stat_io doesn't track. Nor do any > > pre-existing forms of IO statistics. > > > > It seems pretty clear that we should track writeback as well.
Agreed. +1. > > I wonder if it's > > worth doing so for 16? It'd give a more complete picture that way. The > > counter-argument I see is that we didn't track the time for it in existing > > stats either, and that nobody complained - but I suspect that's mostly > > because > > nobody knew to look. > > [RMT hat] > > (sorry for slow reply on this, I've been out for a few days). > > It does sound generally helpful to track writeback to ensure anyone > building around pg_stat_io can see tthe more granular picture. How big > of an effort is this? > Right, I think this is the key factor to decide whether we can get this in PG16 or not. If this is just adding a new column and a few existing stats update calls then it should be okay to get in but if this requires some more complex work then we can probably update the docs. -- With Regards, Amit Kapila.