Re: Feature Request - DDL deployment with logical replication
| От | Craig Ringer |
|---|---|
| Тема | Re: Feature Request - DDL deployment with logical replication |
| Дата | |
| Msg-id | CAMsr+YHgHZNX0JiN1xAdByzcmpiruYh4E+RRRO2UFug2ih+1sg@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: Feature Request - DDL deployment with logical replication (Andres Freund <andres@anarazel.de>) |
| Ответы |
Re: Feature Request - DDL deployment with logical replication
|
| Список | pgsql-hackers |
On 1 April 2018 at 00:57, Andres Freund <andres@anarazel.de> wrote:
On 2018-03-31 22:13:42 +0800, Craig Ringer wrote:
> We'll still need a mechanism to transport them to downstreams (like WAL
> messages) and to send responses upstream. For responses I think we will
> finally want to add a backchannel to the logical replication protocol as
> I've wanted for a long while: downstream can send a COPY message on COPY
> BOTH proto back to upstream, which passes it to a callback on the output
> plugin for the output plugin to act on.
Not necessarily? You can just send out the prepare, wait for all
clients to ack it, and then commit/rollback prepared.
We then lack any mechanism by which you can NACK, saying "I can't apply this".
So upstream will wait indefinitely. I guess we just expect the user to intervene and ROLLBACK if they decide a replica isn't going to get the job done, or have checked the replica's logs and found it can't apply it for some hopefully-sane reason.
It's not like we'd auto-ROLLBACK PREPARED in response to a nack from a downstream anyway, so all we're missing is probably info in the upstream logs about which replica(s) cannot apply it and why.
OK. So it'd be a nice-to-have, but not vital.
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