On 2022-07-01 16:08:48 +0900, Masahiko Sawada wrote: > Yes, my point is that it may be misleading that the subscription stats > are created when a subscription is created.
I think it's important to create stats at that time, because otherwise it's basically impossible to ensure that stats are dropped when a transaction rolls back. If some / all columns should return something else before stats are reported that can be addressed easily by tracking that in a separate field.
> On the other hand, I'm not sure we agreed that the behavior that > Melanie reported is not a problem. The user might get confused since > the subscription stats works differently than other stats when a > reset. Previously, the primary reason why I hesitated to create the > subscription stats when creating a subscription is that CREATE > SUBSCRIPTION (with create_slot = false) can be rolled back. But with > the shmem stats, we can easily resolve it by using > pgstat_create_transactional().
Yep.
> > > The second problem is that the following code in DropSubscription() > > > should be updated: > > > > > > /* > > > * Tell the cumulative stats system that the subscription is getting > > > * dropped. We can safely report dropping the subscription statistics here > > > * if the subscription is associated with a replication slot since we > > > * cannot run DROP SUBSCRIPTION inside a transaction block. Subscription > > > * statistics will be removed later by (auto)vacuum either if it's not > > > * associated with a replication slot or if the message for dropping the > > > * subscription gets lost. > > > */ > > > if (slotname) > > > pgstat_drop_subscription(subid); > > > > > > I think we can call pgstat_drop_subscription() even if slotname is > > > NULL and need to update the comment. > > > > > > > +1. > > > > > IIUC autovacuum is no longer > > > responsible for garbage collection. > > > > > > > Right, this is my understanding as well. > > Thank you for the confirmation.