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
> circle that get's "broken" in order to add/remove the server, right? Or do
> 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
> happends to be down... As I'm understanding it, Mysql's replication would
> survive this scenario. What I'd be getting is the ability to do local
> reads/writes and Mysql would simply propogate my writes. For the most part,
> data latency won't be a big deal for my applications unless we're talking
> 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.
> My initial reading indicates that this tool won't work across different
> 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
--
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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