From: Marcus Bointon
Date: October 27 2011 6:21pm
Subject: Re: Master-Master -> duplicate entry
List-Archive: http://lists.mysql.com/replication/2260
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On 27 Oct 2011, at 19:56, Rick James wrote:

> Synchronous replication has a serious limitation --
> If the second master exists for HA, and the building with both masters =
is hit by a tornado, earthquake, flood, etc, then dual-master did not =
help.
> If you move the other master to a remote location, then the delays to =
do the sync could be unacceptable.

I think this is the target of semi-sync. You replicate to multiple =
slaves, but accept a quorum of confirmed sync responses (say 3 out of =
5). This way you're not going to hang up if a remote server dies. You =
can vary the consistency level on a per-query basis - e.g. you might =
insist on 5/5 for critical schema changes. Cassandra is built on this =
design, for both reads and writes.

I've not tried using it in MySQL yet, but it's there in 5.5: =
http://dev.mysql.com/doc/refman/5.5/en/replication-semisync.html

Marcus
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Marcus Bointon
Synchromedia Limited: Creators of http://www.smartmessages.net/
UK info@hand CRM solutions
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