Re: logical decoding and replication of sequences

On 3/1/22 12:53, Amit Kapila wrote:
> 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?
>

Thanks, that seems like an omission. Will fix.

regards

--
Tomas Vondra
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