On Fri, 26 Jun 2020 at 17:53, Amit Kapila <amit.kapil...@gmail.com> wrote: > > On Fri, Jun 26, 2020 at 11:31 AM Masahiko Sawada > <masahiko.saw...@2ndquadrant.com> wrote: > > > > On Thu, 25 Jun 2020 at 19:35, Amit Kapila <amit.kapil...@gmail.com> wrote: > > > > > > On Tue, Jun 23, 2020 at 6:39 PM Amit Kapila <amit.kapil...@gmail.com> > > > wrote: > > > > > > > > On Tue, Jun 23, 2020 at 3:48 PM Tomas Vondra > > > > <tomas.von...@2ndquadrant.com> wrote: > > > > > > > > > > On Tue, Jun 23, 2020 at 10:58:18AM +0530, Amit Kapila wrote: > > > > > >On Tue, Jun 23, 2020 at 9:32 AM Masahiko Sawada > > > > > ><masahiko.saw...@2ndquadrant.com> wrote: > > > > > >> > > > > > >> On Sun, 21 Jun 2020 at 06:57, Tomas Vondra > > > > > >> <tomas.von...@2ndquadrant.com> wrote: > > > > > >> > > > > > > >> > > > > > > > >> > >What if the decoding has been performed by multiple backends > > > > > >> > >using the > > > > > >> > >same slot? In that case, it will be difficult to make the > > > > > >> > >judgment > > > > > >> > >for the value of logical_decoding_work_mem based on stats. It > > > > > >> > >would > > > > > >> > >make sense if we provide a way to set logical_decoding_work_mem > > > > > >> > >for a > > > > > >> > >slot but not sure if that is better than what we have now. > > > > > >> > > > > > > > >> > > > > > >> I thought that the stats are relevant to what > > > > > >> logical_decoding_work_mem value was but not with who performed > > > > > >> logical > > > > > >> decoding. So even if multiple backends perform logical decoding > > > > > >> using > > > > > >> the same slot, the user can directly use stats as long as > > > > > >> logical_decoding_work_mem value doesn’t change. > > > > > >> > > > > > > Today, I thought about it again, and if we consider the point that > > > logical_decoding_work_mem value doesn’t change much then having the > > > stats at slot-level would also allow computing > > > logical_decoding_work_mem based on stats. Do you think it is a > > > reasonable assumption that users won't change > > > logical_decoding_work_mem for different processes (WALSender, etc.)? > > > > FWIW, if we use logical_decoding_work_mem as a threshold of starting > > of sending changes to a subscriber, I think there might be use cases > > where the user wants to set different logical_decoding_work_mem values > > to different wal senders. For example, setting a lower value to > > minimize the latency of synchronous logical replication to a near-site > > whereas setting a large value to minimize the amount of data sent to a > > far site. > > > > How does setting a large value can minimize the amount of data sent? > One possibility is if there are a lot of transaction aborts and > transactions are not large enough that they cross > logical_decoding_work_mem threshold but such cases shouldn't be many.
Yeah, this is what I meant. I agree that it would not be a common case that the user sets different values for different processes. Based on that assumption, I also think having the stats at slot-level is a good idea. But I might want to have the reset function. Regards, -- Masahiko Sawada http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
