Re: Reporting the commit LSN at commit time

On 2014-08-19 19:59:51 +0900, Fujii Masao wrote:
> On Tue, Aug 19, 2014 at 7:21 PM, Andres Freund <andres(at)2ndquadrant(dot)com> wrote:
> > On 2014-08-19 08:21:10 +0800, Craig Ringer wrote:
> >> On 08/19/2014 01:03 AM, Robert Haas wrote:
> >> > 2. I agree that it's not good to have this get controlled by a GUC.
> >> > If the behavior change is big enough that it's going to break clients,
> >> > adding a GUC isn't a sufficient remedy. If it's not, adding a GUC is
> >> > unnecessary.
> >>
> >> There's plenty of agreement on "not a GUC" - but what about alternatives?
> >
> > What's the problem with the COMMIT WITH (report_lsn on) I've proposed?
> > Reporting the LSN in the command tag? Anything doing transparent
> > failover needs to be aware of transaction boundaries anyway.
>
> So something like transparent failover doesn't work when a client is
> working in auto commit mode? That sounds not good.

I don't think transparent failover + autocommit is a sensible
combination.

> Just idea. What about using NoticeResponse message to report LSN?
> It can be sent basically anytime and this idea doesn't break current
> wire protocol.

I think that'd be horrible from multiple perspectives: a) how to discern
them from regular notice messages b) It's not sent in the same protocol
level message as the COMMIT message. Thus there's scenarios where you
only have the commit, but not the LSN.

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
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