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Re: Core team statement on replication in PostgreSQL

From: Robert Treat <xzilla(at)users(dot)sourceforge(dot)net>
To: Greg Smith <gsmith(at)gregsmith(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com>, Andrew Dunstan <andrew(at)dunslane(dot)net>, pgsql-hackers(at)postgresql(dot)org, Bruce Momjian <bruce(at)momjian(dot)us>, David Fetter <david(at)fetter(dot)org>, Josh Berkus <josh(at)agliodbs(dot)com>, Marko Kreen <markokr(at)gmail(dot)com>
Subject: Re: Core team statement on replication in PostgreSQL
Date: 2008-05-30 19:16:34
Message-ID: 200805301516.34494.xzilla@users.sourceforge.net (view raw or flat)
Thread:
Lists: pgsql-advocacypgsql-hackers
On Thursday 29 May 2008 20:31:31 Greg Smith wrote:
> On Thu, 29 May 2008, Tom Lane wrote:
> > There's no point in having read-only slave queries if you don't have a
> > trustworthy method of getting the data to them.
>
> This is a key statement that highlights the difference in how you're
> thinking about this compared to some other people here.  As far as some
> are concerned, the already working log shipping *is* a trustworthy method
> of getting data to the read-only slaves.  There are plenty of applications
> (web oriented ones in particular) where if you could direct read-only
> queries against a slave, the resulting combination would be a giant
> improvement over the status quo even if that slave was as much as
> archive_timeout behind the master.  That quantity of lag is perfectly fine
> for a lot of the same apps that have read scalability issues.
>
> If you're someone who falls into that camp, the idea of putting the sync
> replication job before the read-only slave one seems really backwards.
>

Just looking at it from an overall market perspective, synchronous log 
shipping pretty much only addresses failover needs, where as read-only slaves 
address both failover and scaling issues. (Note I say address, not solve). 

-- 
Robert Treat
Build A Brighter LAMP :: Linux Apache {middleware} PostgreSQL

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