Re: Core team statement on replication in PostgreSQL

From: Josh Berkus <josh(at)agliodbs(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Bruce Momjian <bruce(at)momjian(dot)us>, Gurjeet Singh <singh(dot)gurjeet(at)gmail(dot)com>, Greg Smith <gsmith(at)gregsmith(dot)com>, "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com>, Andrew Dunstan <andrew(at)dunslane(dot)net>, Robert Treat <xzilla(at)users(dot)sourceforge(dot)net>, pgsql-hackers(at)postgresql(dot)org, David Fetter <david(at)fetter(dot)org>, Marko Kreen <markokr(at)gmail(dot)com>
Subject: Re: Core team statement on replication in PostgreSQL
Date: 2008-06-10 16:01:05
Message-ID: 200806100901.06460.josh@agliodbs.com
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All,

> > For the slave to not interfere with the master at all, we would need to
> > delay application of WAL files on each slave until visibility on that
> > slave allows the WAL to be applied, but in that case we would have
> > long-running transactions delay data visibility of all slave sessions.
>
> Right, but you could segregate out long-running queries to one slave
> server that could be further behind than the others.

I still see having 2 different settings:

Synchronous: XID visibility is pushed to the master. Maintains synchronous
failover, and users are expected to run *1* master to *1* slave for most
installations.

Asynchronous: replication stops on the slave whenever minxid gets out of
synch. Could have multiple slaves, but noticeable lag between master and
slave.

--
Josh Berkus
PostgreSQL @ Sun
San Francisco

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