Re: logical decoding of two-phase transactions

On 2017-03-28 15:32:49 +0100, Simon Riggs wrote:
> On 28 March 2017 at 03:53, Craig Ringer <craig(at)2ndquadrant(dot)com> wrote:
> > On 28 March 2017 at 09:25, Andres Freund <andres(at)anarazel(dot)de> wrote:
> >
> >> If you actually need separate decoding of 2PC, then you want to wait for
> >> the PREPARE to be replicated. If that replication has to wait for the
> >> to-be-replicated prepared transaction to commit prepared, and commit
> >> prepare will only happen once replication happened...
> >
> > In other words, the output plugin cannot decode a transaction at
> > PREPARE TRANSACTION time if that xact holds an AccessExclusiveLock on
> > a catalog relation we must be able to read in order to decode the
> > xact.
>
> Yes, I understand.
>
> The decoding plugin can choose to enable lock_timeout, or it can
> choose to wait for manual resolution, or it could automatically abort
> such a transaction to avoid needing to decode it.

That doesn't solve the problem. You still left with replication that
can't progress. I think that's completely unacceptable. We need a
proper solution to this, not throw our hands up in the air and hope that
it's not going to hurt a whole lot of peopel.

> I don't think its for us to say what the plugin is allowed to do. We
> decided on a plugin architecture, so we have to trust that the plugin
> author resolves the issues. We can document them so those choices are
> clear.

I don't think this is "plugin architecture" related. The output pluging
can't do right here, this has to be solved at a higher level.

- Andres