Message-ID: <4D23D09D.3000207@2ndquadrant.com>
Date: Tue, 04 Jan 2011 20:59:57 -0500
From: Greg Smith <greg@2ndquadrant.com>
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To: Simon Riggs <simon@2ndQuadrant.com>
CC: Josh Berkus <josh@agliodbs.com>,
	Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>,
	Robert Haas <robertmhaas@gmail.com>,
	Hannu Krosing <hannu@2ndquadrant.com>,
	Stefan Kaltenbrunner <stefan@kaltenbrunner.cc>,
	pgsql-hackers@postgresql.org
Subject: Re: Sync Rep Design
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	<4D1DAB14.5000800@enterprisedb.com>	
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	<1294003186.2090.3338.camel@ebony> <4D2366CE.1010705@agliodbs.com>
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Simon Riggs wrote:
> Based upon that series of conversations, I've reworked the design so
> that there is (currently) only a single standby offering sync rep at any
> one time. Other standbys can request to be sync standbys but they only
> become the sync standby if the first one fails. Which was simple to do
> and bridges the challenges of an exactly identified sync standby and the
> fragility of too closely specifying the config.
>   

That seems like a good enough starting point to cover a lot of cases.  
Presuming the two servers each at two sites config that shows up in a 
lot of these discussions, people in the "I need sync to a remote spot" 
can get that, and if that site is unavailable for long enough to be 
kicked out they'll smoothly degrade to sync on a secondary local copy.  
And those who want high performance local sync and best-effort for the 
remote site can configure for that too, and if the local secondary dies 
they'll just degrade to the slow remote commits.

-- 
Greg Smith   2ndQuadrant US    greg@2ndQuadrant.com   Baltimore, MD
PostgreSQL Training, Services and Support        www.2ndQuadrant.us
"PostgreSQL 9.0 High Performance": http://www.2ndQuadrant.com/books