From: Marcus Bointon
Date: April 7 2010 5:24pm
Subject: Re: Circular replication?
List-Archive: http://lists.mysql.com/replication/1872
Message-Id: <57A563AE-C38B-48AA-8566-E88860C4E807@synchromedia.co.uk>
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On 7 Apr 2010, at 18:27, Mike Diehl wrote:

> I assume that I only need to update the master information at the =
point in the=20
> circle that get's "broken" in order to add/remove the server, right?  =
Or do=20
> all of the db servers need to know about the change?

The former - only the affected servers need to know.

> A split read/write scheme will affect reliability if one of the write =
servers=20
> happends to be down...  As I'm understanding it, Mysql's replication =
would=20
> survive this scenario.  What I'd be getting is the ability to do local=20=

> reads/writes and Mysql would simply propogate my writes.  For the most =
part,=20
> data latency won't be a big deal for my applications unless we're =
talking=20
> HOURS. (and we're not, unless something is BAD wrong.)

OK, I can see a problem here; a mysql instance can only be a slave to =
one master. A 'normal' mode of circular replication would be A<->B, =
treating A as the active master (i.e no writes normally go to B, but it =
will all still work if you do). If you have A->B->C->A (C being offsite) =
and C dies, no writes to B will make it back to A. That's a pretty =
fragile setup. You could do active failover to take C out of the loop =
and repoint B at A, however, that's likely to cause data loss if C ever =
comes back.

Replication latency becomes a problem if you do any long transactions. =
If you have a transaction that takes 10 minutes on A, it won't show up =
on C until 30 minutes later (assuming equal server performance).

An A<->B->C arrangement would give you fast local reads, slow writes, =
and avoid the risk of data loss.

> My research has turned up a package called Mysql Multi Master =
Manager(?),mmmm. =20
> My initial reading indicates that this tool won't work across =
different=20
> networks, right?

That's the one - mmm needs to be able to handle floating IPs and emit =
arp packets, which only really makes sense on a LAN.

Marcus
--=20
Marcus Bointon
Synchromedia Limited: Creators of http://www.smartmessages.net/
UK resellers of info@hand CRM solutions
marcus@stripped | http://www.synchromedia.co.uk/



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