Re: pg_receivexlog --status-interval add fsync feedback

> On 10/08/2014 07:23 AM, furuyao(at)pm(dot)nttdata(dot)co(dot)jp wrote:
> >> What set of options would you pass if you want to use it as a
> >> synchronous standby? And if you don't? Could we just have a single
> "--synchronous"
> >> flag, instead of -F and --reply-fsync?
> >
> > If you set "synchronous_commit" as "remote_write", the options would
> be different .
> > The set of options in each case, see the following.
> >
> >
> > Synchronous standby(synchronous_commit=on)
> > --fsync-interval=-1
> > --reply-fsync
> > --slot=slotname
> >
> > Synchronous standby(synchronous_commit=remote_write)
> > --fsync-interval=-1
> > --reply-fsync
> >
> > Asynchronous
> > There are no relative options.
> >
> >
> > Well, if the response time delay(value of
> "--status-interval=interval") is acceptable, "--reply-fsync" is
> unnecessary.
> > Instead of "--reply-fsync", using "--synchronous"(which summarizes
> the "--reply-fsync" and "fsync-interval = -1") might be easy to
> understand. Although, in that case, "--fsync-interval=interval" would
> be fixed value. Isn't there any problem ?
>
> I think we should remove --fsync-interval and --reply-fsync, and just
> have a --synchronous option, which would imply the same behavior you get
> with --fsync-interval=-1 --reply--fsync.
>
> That leaves the question of whether pg_receivexlog should do fsyncs when
> it's not acting as a synchronous standby. There isn't any real need to
> do so. In asynchronous mode, there are no guarantees anyway, and even
> without an fsync, the OS will eventually flush the data to disk.
>
> But we could do even better than that. It would be best if you didn't
> need even the --synchronous flag. The server knows whether the client
> is a synchronous standby or not. It could tell the client.

Thanks for the reply.

If we remove --fsync-interval, resoponse time to user will not be delay.
Although, fsync will be executed multiple times in a short period.
And there is no way to solve the problem without --fsync-interval, what should we do about it?

In asynchronous mode, I think there is no problem since the specification is same with release version.

> The server knows whether the client is a synchronous standby or not.
> It could tell the client.

When notifying the synchronous/asynchronous mode to the client from the server,
do we need to change the format of the Message ?

Regards,

--
Furuya Osamu