Re: Perform streaming logical transactions by background workers and parallel apply
От | Peter Smith |
---|---|
Тема | Re: Perform streaming logical transactions by background workers and parallel apply |
Дата | |
Msg-id | CAHut+PsDcJ6r4a=AvpfDN08tstU2Qwuz+=-h_uECufBmtFbHww@mail.gmail.com обсуждение исходный текст |
Ответ на | Re: Perform streaming logical transactions by background workers and parallel apply (Amit Kapila <amit.kapila16@gmail.com>) |
Список | pgsql-hackers |
On Mon, Aug 22, 2022 at 7:01 PM Amit Kapila <amit.kapila16@gmail.com> wrote: > > On Mon, Aug 22, 2022 at 4:42 AM Peter Smith <smithpb2250@gmail.com> wrote: > > > > On Fri, Aug 19, 2022 at 7:55 PM Amit Kapila <amit.kapila16@gmail.com> wrote: > > > > > > On Fri, Aug 19, 2022 at 3:05 PM Peter Smith <smithpb2250@gmail.com> wrote: > > > > > > > > On Fri, Aug 19, 2022 at 7:10 PM Amit Kapila <amit.kapila16@gmail.com> wrote: > > > > > > > > > > On Fri, Aug 19, 2022 at 2:36 PM Peter Smith <smithpb2250@gmail.com> wrote: > > > > > > > > > > > > Here are my review comments for the v23-0005 patch: > > > > > > > > > > > > ====== > > > > > > > > > > > > Commit Message says: > > > > > > main_worker_pid is Process ID of the main apply worker, if this process is a > > > > > > apply background worker. NULL if this process is a main apply worker or a > > > > > > synchronization worker. > > > > > > The new column can make it easier to distinguish main apply worker and apply > > > > > > background worker. > > > > > > > > > > > > -- > > > > > > > > > > > > Having a column called ‘main_worker_pid’ which is defined to be NULL > > > > > > if the process *is* the main apply worker does not make any sense to > > > > > > me. > > > > > > > > > > > > > > > > I haven't read this part of a patch but it seems to me we have > > > > > something similar for parallel query workers. Refer 'leader_pid' > > > > > column in pg_stat_activity. > > > > > > > > > > > > > IIUC (from the patch 0005 commit message) the intention is to be able > > > > to easily distinguish the worker types. > > > > > > > > > > I think it is only to distinguish between leader apply worker and > > > background apply workers. The tablesync worker can be distinguished > > > based on relid field. > > > > > > > Right. But that's the reason for my question in the first place - why > > implement the patch so that the user still has to jump through hoops > > just to know the worker type information? > > > > I think it is not only to judge worker type but also to know the pid > of each of the workers during parallel apply. Isn't it better to have > both main apply worker pid and parallel apply worker pid as we have > for the parallel query system? > OK, thanks for pointing me to that other view. Now that I see the existing pg_stat_activity already has 'pid' and 'leader_pid' [1], it suddenly seems more reasonable to do similar for this pg_stat_subscription. This background information needs to be conveyed better in the patch 0005 commit message. The current commit message said nothing about trying to be consistent with the existing stats views; it only says this field was added to distinguish more easily between the types of apply workers. ------ [1] https://www.postgresql.org/docs/devel/monitoring-stats.html Kind Regards, Peter Smith. Fujitsu Australia
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