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From: Greg Smith <greg@2ndquadrant.com>
To: Simon Riggs <simon@2ndQuadrant.com>
Cc: Josh Berkus <josh@agliodbs.com>
Cc: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Hannu Krosing <hannu@2ndquadrant.com>
Cc: Stefan Kaltenbrunner <stefan@kaltenbrunner.cc>
Cc: pgsql-hackers@postgresql.org
Subject: Re: Sync Rep Design
Date: Tue, 04 Jan 2011 20:59:57 -0500
Message-ID: <4D23D09D.3000207@2ndquadrant.com> (raw)
In-Reply-To: <1294167105.19612.8276.camel@ebony>
References: <1293729972.1892.23804.camel@ebony>
	<4D1CC47E.7050207@kaltenbrunner.cc>
	<1293735853.1892.24886.camel@ebony>
	<AANLkTi=SvN2KQ1Tzh-tRKcXD0i2FyWFBbbR=kXXdepqN@mail.gmail.com>
	<4D1D8B2F.5070001@2ndquadrant.com>
	<4D1DAB14.5000800@enterprisedb.com>
	<1293796137.1892.37313.camel@ebony>
	<4D1DCF5A.7070808@enterprisedb.com>
	<4D1E4897.1050400@2ndquadrant.com>
	<1293882875.1892.56143.camel@ebony>
	<AANLkTi=yYKvRCvfTprbj=jQDVMrDKUMcate=vCaQobSi@mail.gmail.com>
	<1293975673.2090.464.camel@ebony>
	<4D20ADC5.7070804@enterprisedb.com>
	<1294003186.2090.3338.camel@ebony>
	<4D2366CE.1010705@agliodbs.com>
	<1294167105.19612.8276.camel@ebony>

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




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