Subject: Re: Sync Rep Design
From: Simon Riggs <simon@2ndQuadrant.com>
To: Stefan Kaltenbrunner <stefan@kaltenbrunner.cc>
Cc: Dimitri Fontaine <dimitri@2ndQuadrant.fr>,
	Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>,
	greg@2ndQuadrant.com, Josh Berkus <josh@postgresql.org>,
	Hannu Krosing <hannu@2ndquadrant.com>,
	Robert Haas <robertmhaas@gmail.com>, pgsql-hackers@postgresql.org
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Date: Sat, 01 Jan 2011 17:03:48 +0000
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On Sat, 2011-01-01 at 17:37 +0100, Stefan Kaltenbrunner wrote:
> On 01/01/2011 05:28 PM, Dimitri Fontaine wrote:
> > Stefan Kaltenbrunner<stefan@kaltenbrunner.cc>  writes:
> >> well you keep saying that but to be honest I cannot really even see a
> >> usecase for me - what is "only a random one of a set of servers is sync at
> >> any time and I don't really know which one".
> >
> > It looks easy enough to get to know which one it is.  Surely the primary
> > knows and could update something visible through a system view for
> > users?  This as been asked for before and I was thinking there was a
> > consensus on this.
> 
> well as jeff janes already said - anything that requires the master to 
> still exist is not useful for a desaster.

Nobody has suggested that the master needs to still exist after a
disaster.

>  Consider the now often 
> mentioned 2 sync standby scenario with one standby in the same location 
> and one in a secondary location.
> If you have a desaster(fire,water,explosion,admin fail,...) at the 
> primary location and you have no access to either the master or the 
> standby you will never be sure that the standby on the secondary 
> location is actually "in sync" - it could be but you will never know if 
> you lost that 1B$ invoice just commited on the master and the closeby 
> standby and therefor confirmed to the client...

I've never suggested you configure your systems like that. It would of
course be stupid.

This is not a sensible technical discussion. I'll go back to coding.

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