Hi, On Fri, Feb 28, 2025 at 02:41:34PM +0900, Michael Paquier wrote: > On Wed, Feb 26, 2025 at 09:48:50AM +0000, Bertrand Drouvot wrote: > > Yeah I think that makes sense, done that way in the attached. > > > > Speaking about physical walsender, I moved the test to 001_stream_rep.pl > > instead > > (would also fail without the fix). > > Hmm. I was doing some more checks with this patch, and on closer look > I am wondering if the location you have chosen for the stats reports > is too aggressive: this requires a LWLock for the WAL sender backend > type taken in exclusive mode, with each step of WalSndLoop() taken > roughly each time a record or a batch of records is sent. A single > installcheck with a primary/standby setup can lead to up to 50k stats > report calls.
Yeah, what I can observe (installcheck with a primary/standby): - extras flush are called about 70K times. Among those 70K: - about 575 are going after the "have_iostats" check in pgstat_io_flush_cb() - about 575 are going after the PendingBackendStats pg_memory_is_all_zeros() check in pgstat_flush_backend() (makes sense due to the above) - about 575 are going after the PendingBackendStats.pending_io pg_memory_is_all_zeros() check in pgstat_flush_backend_entry_io() (makes sense due to the above) It means that only a very few of them are "really" flushing IO stats. > With smaller records, the loop can become hotter, can't it? Also, > there can be a high number of WAL senders on a single node, and I've > heard of some customers with complex logical decoding deployments with > dozens of logical WAL senders. Isn't there a risk of having this code > path become a point of contention? It seems to me that we should > benchmark this change more carefully, perhaps even reduce the > frequency of the report calls. That sounds a good idea to measure the impact of those extra calls and see if we'd need to mitigate the impacts. I'll collect some data. Regards, -- Bertrand Drouvot PostgreSQL Contributors Team RDS Open Source Databases Amazon Web Services: https://aws.amazon.com
