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
--
Marcus Bointon
Synchromedia Limited: Creators of http://www.smartmessages.net/
UK info@hand CRM solutions
marcus@stripped | http://www.synchromedia.co.uk/
