Horton

Re: Skipping logical replication transactions on subscriber side

Greg Nancarrow <gregn4422@gmail.com>

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From: Greg Nancarrow <gregn4422@gmail.com>
To: vignesh C <vignesh21@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, "tanghy.fnst@fujitsu.com" <tanghy.fnst@fujitsu.com>, "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>, "osumi.takamichi@fujitsu.com" <osumi.takamichi@fujitsu.com>, Alexey Lesovsky <lesovsky@gmail.com>, Peter Eisentraut <peter.eisentraut@enterprisedb.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2021-11-19T06:32:23Z
Lists: pgsql-hackers 
On Fri, Nov 19, 2021 at 4:39 PM vignesh C <vignesh21@gmail.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

Commits

  1. Test ALIGNOF_DOUBLE==4 compatibility under ALIGNOF_DOUBLE==8.

  2. Reorder subskiplsn in pg_subscription to avoid alignment issues.

  3. Add ALTER SUBSCRIPTION ... SKIP.

  4. Optionally disable subscriptions on error.

  5. Update docs of logical replication for commit 8d74fc96db.

  6. Respect permissions within logical replication.

  7. Fix regression test failure caused by commit 8d74fc96db.

  8. Add a view to show the stats of subscription workers.

  9. Add logical change details to logical replication worker errcontext.

  10. Rename LOGICAL_REP_MSG_STREAM_END to LOGICAL_REP_MSG_STREAM_STOP.

  11. Fix typo in protocol.sgml.

  12. Remove unused argument in apply_handle_commit_internal().

  13. Fix replication of in-progress transactions in tablesync worker.

  14. Reorder pg_sequence columns to avoid alignment issue