Re: logical decoding and replication of sequences

On Mon, Feb 28, 2022 at 5:16 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Sat, Feb 12, 2022 at 6:04 AM Tomas Vondra
> <tomas(dot)vondra(at)enterprisedb(dot)com> wrote:
> >
> > On 2/10/22 19:17, Tomas Vondra wrote:
> > > I've polished & pushed the first part adding sequence decoding
> > > infrastructure etc. Attached are the two remaining parts.
> > >
> > > I plan to wait a day or two and then push the test_decoding part. The
> > > last part (for built-in replication) will need more work and maybe
> > > rethinking the grammar etc.
> > >
> >
> > I've pushed the second part, adding sequences to test_decoding.
> >
>
> The test_decoding is failing randomly in the last few days. I am not
> completely sure but they might be related to this work. The two of
> these appears to be due to the same reason:
> https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=skink&dt=2022-02-25%2018%3A50%3A09
> https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=locust&dt=2022-02-17%2015%3A17%3A07
>
> TRAP: FailedAssertion("prev_first_lsn < cur_txn->first_lsn", File:
> "reorderbuffer.c", Line: 1173, PID: 35013)
> 0 postgres 0x00593de0 ExceptionalCondition + 160\\0
>

While reviewing the code for this, I noticed that in
sequence_decode(), we don't call ReorderBufferProcessXid to register
the first known lsn in WAL for the current xid. The similar functions
logicalmsg_decode() or heap_decode() do call ReorderBufferProcessXid
even if they decide not to queue or send the change. Is there a reason
for not doing the same here? However, I am not able to deduce any
scenario where lack of this will lead to such an Assertion failure.
Any thoughts?

--
With Regards,
Amit Kapila.