Re: Adding REPACK [concurrently]

Antonin Houska <ah(at)cybertec(dot)at> wrote:

> Mihail Nikalayeu <mihailnikalayeu(at)gmail(dot)com> wrote:
>
> >Antonin Houska <ah(at)cybertec(dot)at>:
> >>
> >> As the test runs pgbench with --client=30 and the default value of
> >> max_worker_processes is 8, I'm not sure this is a leak. I've increased this
> >> parameter I couldn't see the error anymore.
> >
> > Hm, as far as I remember only single repack may be executed in test (because
> > of locking on test itself and also REPACK).
>
> The only problem is that the logical decoding system needs to wait during the
> setup for all the running transactions to finish. So if REPACK (CONCURRENTLY)
> is already running, the next execution will not start until the first is done.
>
> However, that does not restrict the REPACK decoding workers from starting.
>
> >> I agree that this is due to the missing MVCC safety feature. I commented that
> >> check in the script for now.
> >
> > I don't think so. In case of non-MVCC safety we should see 0 or correct sum. But script failed with 490588...
> > But should see 500500 (if I correctly calculated sum of numbers from 1 to 1000)...
>
> I was referring to your statement "It may be 0 because non-MVCC
> safe". Regarding the non-zero values, I think I finally understand the issue
> and even could reproduce some weird behavior using debugger. Since it also
> affects logical replication, I'll provide more details (and hopefully propose
> a patch) in a separate thread early next week.

This is the report:

https://www.postgresql.org/message-id/85833.1768840165%40localhost

--
Antonin Houska
Web: https://www.cybertec-postgresql.com