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: "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>, vignesh C <vignesh21@gmail.com>, Greg Nancarrow <gregn4422@gmail.com>, "tanghy.fnst@fujitsu.com" <tanghy.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: 2021-12-01T04:00:18Z
Lists: pgsql-hackers 
On Wed, Dec 1, 2021 at 9:12 AM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
> On Wed, Dec 1, 2021 at 12:22 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> >
> > On Wed, Dec 1, 2021 at 8:24 AM houzj.fnst@fujitsu.com
> > <houzj.fnst@fujitsu.com> wrote:
> > >
> > > I have a question about the testcase (I could be wrong here).
> > >
> > > Is it possible that the race condition happen between apply worker(test_tab1)
> > > and table sync worker(test_tab2) ? If so, it seems the error("replication
> > > origin with OID") could happen randomly until we resolve the conflict.
> > > Based on this, for the following code:
> > > -----
> > >     # Wait for the error statistics to be updated.
> > >     my $check_sql = qq[SELECT count(1) > 0 ] . $part_sql;
> > >     $node->poll_query_until(
> > >         'postgres', $check_sql,
> > > ) or die "Timed out while waiting for statistics to be updated";
> > >
> > > * [1] *
> > >
> > >     $check_sql =
> > >         qq[
> > > SELECT subname, last_error_command, last_error_relid::regclass,
> > > last_error_count > 0 ] . $part_sql;
> > >     my $result = $node->safe_psql('postgres', $check_sql);
> > >     is($result, $expected, $msg);
> > > -----
> > >
> > > Is it possible that the error("replication origin with OID") happen again at the
> > > place [1]. In this case, the error message we have checked could be replaced by
> > > another error("replication origin ...") and then the test fail ?
> > >
> >
> > Once we get the "duplicate key violation ..." error before * [1] * via
> > apply_worker then we shouldn't get replication origin-specific error
> > because the origin set up is done before starting to apply changes.
>
> Right.
>
> > Also, even if that or some other happens after * [1] * because of
> > errmsg_prefix check it should still succeed.
>
> In this case, the old error ("duplicate key violation ...") is
> overwritten by a new error (e.g., connection error. not sure how
> possible it is)
>

Yeah, or probably some memory allocation failure. I think the
probability of such failures is very low but OTOH why take chance.

> and the test fails because the query returns no
> entries, no?
>

Right.

> If so, the result from the second check_sql is unstable
> and it's probably better to check the result only once. That is, the
> first check_sql includes the command and we exit from the function
> once we confirm the error entry is expectedly updated.
>

Yeah, I think that should be fine.

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