Re: logical decoding of two-phase transactions

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.

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.

This doesn't differ in any respect from any other resource it might
need yet cannot obtain.

--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services