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Re: Sync Rep v17

From: Simon Riggs <simon(at)2ndQuadrant(dot)com>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, pgsql-hackers(at)postgresql(dot)org, Daniel Farina <daniel(at)heroku(dot)com>
Subject: Re: Sync Rep v17
Date: 2011-02-28 21:12:42
Message-ID: 1298927562.12992.1948.camel@ebony (view raw or whole thread)
Lists: pgsql-hackers
On Sat, 2011-02-19 at 22:52 -0500, Robert Haas wrote:
> On Sat, Feb 19, 2011 at 3:28 AM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> > First, we should be clear to explain that you are referring to the fact
> > that the request
> >  synchronous_commit = off
> >  synchronous_replication = on
> > makes no sense in the way the replication system is currently designed,
> > even though it is a wish-list item to make it work in 9.2+
> What exactly do you mean by "make it work"?  We can either (1) wait
> for the local commit and the remote commit (synchronous_commit=on,
> synchronous_replication=on), (2) wait for the local commit only
> (synchronous_commit=on, synchronous_replication=off), or (3) wait for
> neither (synchronous_commit=off, synchronous_replication=off).
> There's no fourth possible behavior, AFAICS.

Currently, no, since as we discussed earlier we currently need to fsync
WAL locally before it gets sent to standby.

> The question is whether synchronous_commit=off,
> synchronous_replication=on should behave like (1) or (3)

Yes, that is the right question.

> You have it as #1; I'm arguing
> it should be #3.  I realize it's an arguable point; I'm just arguing
> for what makes most sense to me.

Various comments follow on thread. We can pick this up once we've
committed the main patch.

 Simon Riggs 
 PostgreSQL Development, 24x7 Support, Training and Services

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