| From: | Greg Nancarrow <gregn4422(at)gmail(dot)com> |
|---|---|
| To: | vignesh C <vignesh21(at)gmail(dot)com> |
| Cc: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, "tanghy(dot)fnst(at)fujitsu(dot)com" <tanghy(dot)fnst(at)fujitsu(dot)com>, "houzj(dot)fnst(at)fujitsu(dot)com" <houzj(dot)fnst(at)fujitsu(dot)com>, "osumi(dot)takamichi(at)fujitsu(dot)com" <osumi(dot)takamichi(at)fujitsu(dot)com>, Alexey Lesovsky <lesovsky(at)gmail(dot)com>, Peter Eisentraut <peter(dot)eisentraut(at)enterprisedb(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Skipping logical replication transactions on subscriber side |
| Date: | 2021-11-19 06:32:23 |
| Message-ID: | CAJcOf-fQNrHg4NfCwATwF-jn0rpWDK6Ot_cJsczCzDGmFLkY4g@mail.gmail.com |
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On Fri, Nov 19, 2021 at 4:39 PM vignesh C <vignesh21(at)gmail(dot)com> wrote:
>
> Since the statistics collector process uses UDP socket, the sequencing
> of the messages is not guaranteed. Will there be a problem if
> Subscription is dropped and stats collector receives
> PGSTAT_MTYPE_SUBSCRIPTIONPURGE first and the subscription worker entry
> is removed and then receives PGSTAT_MTYPE_SUBWORKERERROR(this order
> can happen because of UDP socket). I'm not sure if the Assert will be
> a problem in this case. If this scenario is possible we could just
> silently return in that case.
>
Given that the message sequencing is not guaranteed, it looks like
that Assert and the current code after it won't handle that scenario
well. Silently returning if subwentry is NULL does seem like the way
to deal with that possibility.
Doesn't this possibility of out-of-sequence messaging due to UDP
similarly mean that "first_error_time" and "last_error_time" may not
be currently handled correctly?
Regards,
Greg Nancarrow
Fujitsu Australia
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