Re: Some pgq table rewrite incompatibility with logical decoding?

Hi,

On 2018-06-25 10:37:18 -0500, Jeremy Finzel wrote:
> I am hoping someone here can shed some light on this issue - I apologize if
> this isn't the right place to ask this but I'm almost some of you all were
> involving in pgq's dev and might be able to answer this.
>
> We are actually running 2 replication technologies on a few of our dbs,
> skytools and pglogical. Although we are moving towards only using logical
> decoding-based replication, right now we have both for different purposes.
>
> There seems to be a table rewrite happening on table pgq.event_58_1 that
> has happened twice, and it ends up in the decoding stream, resulting in the
> following error:
>
> ERROR,XX000,"could not map filenode ""base/16418/1173394526"" to relation
> OID"
>
> In retracing what happened, we discovered that this relfilenode was
> rewritten. But somehow, it is ending up in the logical decoding stream as
> is "undecodable". This is pretty disastrous because the only way to fix it
> really is to advance the replication slot and lose data.
>
> The only obvious table rewrite I can find in the pgq codebase is a truncate
> in pgq.maint_rotate_tables.sql. But there isn't anything surprising
> there. If anyone has any ideas as to what might cause this so that we
> could somehow mitigate the possibility of this happening again until we
> move off pgq, that would be much appreciated.

I suspect the issue might be that pgq does some updates to catalog
tables. Is that indeed the case?

Greetings,

Andres Freund