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From: Simon Riggs <simon@2ndQuadrant.com>
To: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>
Cc: Kevin Grittner <Kevin.Grittner@wicourts.gov>
Cc: MARK CALLAGHAN <mdcallag@gmail.com>
Cc: Markus Wanner <markus@bluegap.ch>
Cc: Alvaro Herrera <alvherre@commandprompt.com>
Cc: Andrew Dunstan <andrew@dunslane.net>
Cc: Aidan Van Dyk <aidan@highrise.ca>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Re: [COMMITTERS] pgsql: Efficient transaction-controlled synchronous replication.
Date: Fri, 18 Mar 2011 16:19:31 +0000
Message-ID: <1300465171.18619.15193.camel@ebony> (raw)
In-Reply-To: <4D837EA2.2070205@enterprisedb.com>
References: <E1PwMns-00047O-UU@gemulon.postgresql.org>
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	<1299454125.1696.6138.camel@ebony>
	<4D74896C.5030402@enterprisedb.com>
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	<AANLkTinkzJ=UrLbThZy2KeQg+SjwYqj2r0mDomMwirB7@mail.gmail.com>
	<4D74F3AE.9000802@dunslane.net>
	<4D74FDEC.5040406@enterprisedb.com>
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	<4D832571.5030808@bluegap.ch>
	<AANLkTi=B+cWE-pQJQM=zoA9=Zr25W7zPPMFvvBe11O4E@mail.gmail.com>
	<1300457958.18619.13780.camel@ebony>
	<4D832B4D020000250003BA98@gw.wicourts.gov>
	<4D837EA2.2070205@enterprisedb.com>

On Fri, 2011-03-18 at 17:47 +0200, Heikki Linnakangas wrote:
> On 18.03.2011 16:52, Kevin Grittner wrote:
> > Simon Riggs<simon@2ndQuadrant.com>  wrote:
> >
> >> In PostgreSQL other users cannot observe the commit until an
> >> acknowledgement has been received.
> >
> > Really?  I hadn't picked up on that.  That makes for a lot of
> > complication on crash-and-recovery of a master, but if we can pull
> > it off, that's really cool.  If we do that and MySQL doesn't, we
> > definitely don't want to use the same terminology they do, which
> > would imply the same behavior.
> 
> To be clear: other users cannot observe the commit until standby 
> acknowledges it - unless the master crashes while waiting for the 
> acknowledgment. If that happens, the commit will be visible to everyone 
> after recovery.

No, only in the case where you choose not to failover to the standby
when you crash, which would be a fairly strange choice after the effort
to set up the standby. In a correctly configured and operated cluster
what I say above is fully correct and needs no addendum.

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




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  Cc: simon@2ndQuadrant.com, heikki.linnakangas@enterprisedb.com, Kevin.Grittner@wicourts.gov, mdcallag@gmail.com, markus@bluegap.ch, alvherre@commandprompt.com, andrew@dunslane.net, aidan@highrise.ca, pgsql-hackers@postgresql.org
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