Re: BUG #16643: PG13 - Logical replication - initial startup never finishes and gets stuck in startup loop

On Wed, Nov 18, 2020 at 2:12 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Wed, Nov 18, 2020 at 11:19 AM Peter Smith <smithpb2250@gmail.com> wrote:
> >
> > On Wed, Nov 18, 2020 at 3:17 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> > > > To cut a long story short, a tablesync worker CAN in fact end up
> > > > processing (e.g. apply_dispatch) streaming messages.
> > > > So the tablesync worker CAN get into the apply_handle_stream_commit.
> > > > And this scenario, albeit rare, will crash.
> > > >
> > >
> > > Thank you for reproducing this issue. Dilip, Peter, is anyone of you
> > > interested in writing a fix for this?
> >
> > Hi Amit.
> >
> > FYI - Sorry, I am away/offline for the next 5 days.
> >
> > However, if this bug still remains unfixed after next Tuesday then I
> > can look at it then.
> >
>
> Fair enough. Let's see if Dilip or I can get a chance to look into
> this before that.
>
> > ---
> >
> > IIUC there are 2 options:
> > 1) Disallow streaming for the tablesync worker.
> > 2) Make streaming work for the tablesync worker.
> >
> > I prefer option (a) not only because of the KISS principle, but also
> > because this is how the tablesync worker was previously thought to
> > behave anyway. I expect this fix may be like the code that Dilip
> > already posted [1]
> > [1] https://www.postgresql.org/message-id/CAFiTN-uUgKpfdbwSGnn3db3mMQAeviOhQvGWE_pC9icZF7VDKg%40mail.gmail.com
> >
> > OTOH, option (b) fix may or may not be possible (I don't know), but I
> > have doubts that it is worthwhile to consider making a special fix for
> > a scenario which so far has never been reproduced outside of the
> > debugger.
> >
>
> I would prefer option (b) unless the fix is not possible due to design
> constraints. I don't think it is a good idea to make tablesync workers
> behave differently unless we have a reason for doing so.
>

Okay, I will analyze this and try to submit my finding today.

-- 
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com