On Sat, Mar 20, 2021 at 9:25 AM Amit Kapila <amit.kapil...@gmail.com> wrote: > > On Sat, Mar 20, 2021 at 12:22 AM Andres Freund <and...@anarazel.de> wrote: > > > > And then more generally about the feature: > > - If a slot was used to stream out a large amount of changes (say an > > initial data load), but then replication is interrupted before the > > transaction is committed/aborted, stream_bytes will not reflect the > > many gigabytes of data we may have sent. > > > > We can probably update the stats each time we spilled or streamed the > transaction data but it was not clear at that stage whether or how > much it will be useful. > > > - I seems weird that we went to the trouble of inventing replication > > slot stats, but then limit them to logical slots, and even there don't > > record the obvious things like the total amount of data sent. > > > > Won't spill_bytes and stream_bytes will give you the amount of data sent? > > > > > I think the best way to address the more fundamental "pgstat related" > > complaints is to change how replication slot stats are > > "addressed". Instead of using the slots name, report stats using the > > index in ReplicationSlotCtl->replication_slots. > > > > That removes the risk of running out of "replication slot stat slots": > > If we loose a drop message, the index eventually will be reused and we > > likely can detect that the stats were for a different slot by comparing > > the slot name. > > > > This idea is worth exploring to address the complaints but what do we > do when we detect that the stats are from the different slot? It has > mixed of stats from the old and new slot. We need to probably reset it > after we detect that. >
What if the user created a slot with the same name after dropping the slot and it has used the same index. I think chances are less but still a possibility, but maybe that is okay. > What if after some frequency (say whenever we > run out of indexes) we check whether the slots we are maintaining is > pgstat.c have some stale slot entry (entry exists but the actual slot > is dropped)? > A similar drawback (the user created a slot with the same name after dropping it) exists with this as well. -- With Regards, Amit Kapila.
