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Re: Bidirectional replication

From: Simon Riggs <simon(at)2ndQuadrant(dot)com>
To: Sim Zacks <sim(at)compulab(dot)co(dot)il>
Cc: pgsql-general <pgsql-general(at)postgresql(dot)org>
Subject: Re: Bidirectional replication
Date: 2011-05-03 09:19:09
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Lists: pgsql-general
On Tue, May 3, 2011 at 7:31 AM, Sim Zacks <sim(at)compulab(dot)co(dot)il> wrote:

> I have heard good things about Bucardo, though I haven't tried it myself
> yet. I was warned that it would be risky to have 2 masters that have the
> same tables modified in both because of issues such as delayed sync, race
> conditions and other such goodies that may corrupt the meaning of the data.

Just to be clear and fair to Bucardo, I would add a few points.

All multi-master replication solutions that use an optimistic
mechanism require "conflict resolution" cases and code. This is the
same with SQLServer and Oracle etc.. Referring to a well known problem
as a race condition seems to introduce doubt and fear into a situation
that is well understood. Bucardo does offer hooks for conflict
resolution to allow you to program around the issues.

So if I felt that multi-master replication was the right way to go for
a solution, Bucardo is a good choice.

Just to add other info: if multi-master replication uses pessimistic
coherence, then the coherence mechanism can also be a source of
contention and/or cause the need for alternative kinds of conflict

 Simon Riggs         
 PostgreSQL Development, 24x7 Support, Training & Services

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