Subject: Re: [COMMITTERS] pgsql: Efficient transaction-controlled
	synchronous replication.
From: Simon Riggs <simon@2ndQuadrant.com>
To: Fujii Masao <masao.fujii@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>,
	PostgreSQL-development <pgsql-hackers@postgresql.org>
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Date: Fri, 18 Mar 2011 07:52:07 +0000
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On Fri, 2011-03-18 at 14:45 +0900, Fujii Masao wrote:
> On Fri, Mar 18, 2011 at 2:52 AM, Robert Haas <robertmhaas@gmail.com> wrote:
> > On Thu, Mar 10, 2011 at 3:04 PM, Robert Haas <robertmhaas@gmail.com> wrote:
> >>> -                       /* Let the master know that we received some data. */
> >>> -                       XLogWalRcvSendReply();
> >>> -                       XLogWalRcvSendHSFeedback();
> >>>
> >>> This change completely eliminates the difference between write_location
> >>> and flush_location in pg_stat_replication. If this change is reasoable, we
> >>> should get rid of write_location from pg_stat_replication since it's useless.
> >>> If not, this change should be reverted. I'm not sure whether monitoring
> >>> the difference between write and flush locations is useful. But I guess that
> >>> someone thought so and that code was added.
> >>
> >> I could go either way on this but clearly we need to do one or the other.
> >
> > I'm not really sure why this was part of the synchronous replication
> > patch, but after mulling it over I think it's probably right to rip
> > out write_location completely.  There shouldn't ordinarily be much of
> > a gap between write location and flush location, so it's probably not
> > worth the extra network overhead to keep track of it.  We might need
> > to re-add some form of this in the future if we have a version of
> > synchronous replication that only waits for confirmation of receipt
> > rather than for confirmation of flush, but we don't have that in 9.1,
> > so why bother?
> >
> > Barring objections, I'll go do that.
> 
> I agree to get rid of write_location.

No, don't remove it.

We seem to be just looking for things to tweak without any purpose.
Removing this adds nothing for us.

We will have the column in the future, it is there now, so leave it.

-- 
 Simon Riggs           http://www.2ndQuadrant.com/books/
 PostgreSQL Development, 24x7 Support, Training and Services