Re: Stopping logical replication protocol

> Vladimir? I'm running out of time to spend on this at least until the next
CF. Think you can make these changes?

Yes, I can. But I thinks It should be discuss first.

> Terminating COPY BOTH with ERRCODE_QUERY_CANCELED seems fine. If it
> was expecting the error the client can Sync and do whatever it next
> wants to do on the walsender protocol, or bail out nicely.

Do you want return CopyFail with ERRCODE_QUERY_CANCELED instead of CopyDone
on client initialized stop replication?

> Hm, I'm *VERY* doubtful about doing this via yet another callback. Why
> don't we just error out in the prepare write callback?

But what about scenario when output plugin collect changes in memory with
some transformation and send it only inside commit_cb?
It means that OutputPluginPrepareWrite will not execute until end
transaction and we face with too long stops replication when decodes huge
transaction.

2016-10-05 13:06 GMT+03:00 Craig Ringer <craig(at)2ndquadrant(dot)com>:

> On 5 October 2016 at 05:14, Andres Freund <andres(at)anarazel(dot)de> wrote:
> > Hi,
> >
> > On 2016-09-23 13:01:27 +0800, Craig Ringer wrote:
> >> From f98f2388c57d938ebbe07ccd2dbe02138312858f Mon Sep 17 00:00:00 2001
> >> From: Vladimir Gordiychuk <folyga(at)gmail(dot)com>
> >> Date: Wed, 7 Sep 2016 00:39:18 +0300
> >> Subject: [PATCH 2/4] Client-initiated CopyDone during transaction
> decoding in
> >> walsender
> >>
> >> The prior patch caused the walsender to react to a client-initiated
> >> CopyDone while it's in the WalSndLoop. That's not enough to let clients
> >> end logical decoding mid-transaction because we loop in
> ReorderBufferCommit
> >> during decoding of a transaction without ever returning to WalSndLoop.
> >>
> >> Allow breaking out of ReorderBufferCommit by detecting that client
> >> input has requested an end to COPY BOTH mode, so clients can abort
> >> decoding mid-transaction.
> >
> > Hm, I'm *VERY* doubtful about doing this via yet another callback. Why
> > don't we just error out in the prepare write callback?
>
> That's sensible.
>
> > I don't think it's a good idea to return a non-error state if a command
> > is interrupted in the middle. We might already have sent a partial
> > transaction or such. Also compare this to interrupting a query - we
> > don't just returning rows, we error out.
>
> Good point. It's not usually visible to the user because if it's a
> client-initiated cancel the client will generally consume the error,
> but there's still an error generated.
>
> Terminating COPY BOTH with ERRCODE_QUERY_CANCELED seems fine. If it
> was expecting the error the client can Sync and do whatever it next
> wants to do on the walsender protocol, or bail out nicely.
>
> Vladimir? I'm running out of time to spend on this at least until the
> next CF. Think you can make these changes?
>
>
> --
> Craig Ringer http://www.2ndQuadrant.com/
> PostgreSQL Development, 24x7 Support, Training & Services
>