Horton

Re: Skipping logical replication transactions on subscriber side

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Masahiko Sawada <sawada.mshk@gmail.com>
Cc: Peter Eisentraut <peter.eisentraut@enterprisedb.com>, "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>, "tanghy.fnst@fujitsu.com" <tanghy.fnst@fujitsu.com>, "osumi.takamichi@fujitsu.com" <osumi.takamichi@fujitsu.com>, Alexey Lesovsky <lesovsky@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>, Greg Nancarrow <gregn4422@gmail.com>
Date: 2021-10-01T05:50:20Z
Lists: pgsql-hackers 
On Fri, Oct 1, 2021 at 6:30 AM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
> On Fri, Oct 1, 2021 at 5:05 AM Peter Eisentraut
> <peter.eisentraut@enterprisedb.com> wrote:
> >
> > Also, what happens when you forget to reset the xid after it has passed?
> >   Will it get skipped again after wraparound?
>
> Yes.
>

Aren't we resetting the skip_xid once we skip that transaction in
stop_skipping_changes()? If so, it shouldn't be possible to skip it
again after the wraparound. Am I missing something?

Now, if the user has wrongly set some XID which we can't skip as that
is already in past or something like that then I think it is the
user's problem and that's why it can be done only by super users. I
think we have even thought of protecting that via cross-checking with
the information in view but as the view data is lossy, we can't rely
on that. I think users can even set some valid XID that never has any
error and we will still skip it which is what can be done today also
by pg_replication_origin_advance(). I am not sure if we can do much
about such scenarios except to carefully document them.

-- 
With Regards,
Amit Kapila.

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