Re: synchronous_commit = apply

On Tue, Sep 8, 2015 at 1:11 AM, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>
wrote:

> On Thu, Sep 3, 2015 at 12:02 AM, Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
> wrote:
>>
>> One idea is to change the standby so that it manages the locations
>> that the backends in "apply" mode are waiting for in the master,
>> and to make the startup process wake the walreceiver up whenever
>> the replay location reaches either of those locations. In this idea,
>> walreceiver sends back the "apply" location to the master only when
>> needed.
>>
>
> Hmm. So maybe commit records could have a flag saying 'someone is waiting
> for this to commit to apply', and the startup process's apply loop would
> only bother to signal the walreceiver if it sees that flag. I will try
> that.
>

Here is a version that does that, using a bit in xinfo to request apply
feedback from standbys when running with synchronous_commit = apply.

I am not very happy with the way that xact_redo communicates with the main
apply loop when it sees that bit, through calls to
XLogAppliedSynchronousCommit (essentially a global variable), but I
couldn't immediately see a better way to get information out of xact_redo
into the apply loop without changing the rm_redo interface. Perhaps xinfo
is the wrong place for that information. Thoughts?

--
Thomas Munro
http://www.enterprisedb.com