Re: ERROR: no known snapshots

On August 25, 2018 4:43:03 PM GMT+02:00, Andres Freund <andres(at)anarazel(dot)de> wrote:
>On 2018-08-25 07:04:14 +0000, Julien Riou wrote:
>> Hello,
>>
>> We have few highly available clusters with patroni managing
>PostgreSQL
>> 9.6 (pgdg on debian stretch). We use logical decoding with wal2json
>to
>> stream data to a remote platform. On a majority of clusters, it works
>> like a charm. But for one, we have the following error right after
>> decoding start:
>>
>> [1353-1] LOG: starting logical decoding for slot "*****"
>> [1353-2] DETAIL: streaming transactions committing after
>321/292C06F0, reading WAL from 321/28BA9898
>> [1354-1] LOG: logical decoding found consistent point at
>321/28BA9898
>> [1354-2] DETAIL: There are no running transactions.
>> [1355-1] ERROR: no known snapshots
>> [1355-2] CONTEXT: slot "*****", output plugin "wal2json", in the
>change callback, associated LSN 321/2A985A30
>>
>> The only reference of the "no known snapshots" error is in PostgreSQL
>source
>> code:
>>
>https://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=src/backend/access/heap/tuptoaster.c;h=ade4bd142dfbd7ef3340495b06d1041e4032a17f;hb=ca3489e768990e32096f0f24d46d5f0b8b70cff4#l2320
>>
>> Do you know what can cause this error?
>
>Any chance that you're specifying the "include_unchanged_toast" option?
>I briefly looked over wal2json (which isn't part of PG) and as far as I
>can tell that option simply can't work correctly, and would cause
>errors
>like the above.
>
>Greetings,
>
>Andres Freund

We were troubleshooting network, load balancing, patroni but we missed wal2json. There's even an issue on their project with our problem: https://github.com/eulerto/wal2json/issues/74

Many thanks for your insights,

Julien