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From:Marcus Bointon Date:April 7 2010 5:24pm
Subject:Re: Circular replication?
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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 
> 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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Thread
Circular replication?Mike Diehl7 Apr
  • Re: Circular replication?Marcus Bointon7 Apr
    • Re: Circular replication?Mike Diehl7 Apr
      • Re: Circular replication?Marcus Bointon7 Apr
        • Re: Circular replication?Mike Diehl7 Apr
      • Re: Circular replication?Andrew Garner7 Apr
        • Re: Circular replication?Max Schubert7 Apr
          • Re: Circular replication?Mike Diehl7 Apr
            • Re: Circular replication?Max Schubert7 Apr
  • Re: Circular replication?Ben Mildren7 Apr