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Re: Re: [COMMITTERS] pgsql: Efficient transaction-controlled synchronous replication.

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>
Cc: Simon Riggs <simon(at)2ndquadrant(dot)com>, Markus Wanner <markus(at)bluegap(dot)ch>, Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Andrew Dunstan <andrew(at)dunslane(dot)net>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, MARK CALLAGHAN <mdcallag(at)gmail(dot)com>, Aidan Van Dyk <aidan(at)highrise(dot)ca>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Re: [COMMITTERS] pgsql: Efficient transaction-controlled synchronous replication.
Date: 2011-03-18 21:43:32
Message-ID: AANLkTin3y0VzPADjNmXYWF5t_ou7ywqHARJhaxbQ=sTR@mail.gmail.com (view raw or flat)
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On Fri, Mar 18, 2011 at 5:24 PM, Kevin Grittner
<Kevin(dot)Grittner(at)wicourts(dot)gov> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
>> Since the current solution is intended to support data-loss-free
>> failover, but NOT to guarantee a consistent view of the world from
>> a SQL level, I doubt it's worth paying any price for this.
>
> Well, that brings us back to the question of why we would want to
> suppress the view of the data on the master until the replica
> acknowledges the commit.  It *is* committed on the master, we're
> just holding off on telling the committer about it until we can
> honor the guarantee of replication.  If it can be seen on the
> replica before the committer get such acknowledgment, why not on the
> master?

Well, the idea is that we don't want to let people depend on the value
until it's guaranteed to be durably committed.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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