Re: Master-Master replication for wide area configurations

[Anders Karlsson]

Michael!

    The answer is probably no. What Master-Master is about is 
replication with conflict detection / resolution. This is in CGE to 
allow several MySQL Cluster setup to replicate between them. The 
mechanism is the same MySQL Replication you are already using, baically, 
but with some features being added. It is still asynchronous though.
    In your case I'd think hard about if I really want synchronous 
replication in a WAN. If you want real-time (I assume here that you want 
synchronous), you should think hard about the consequences of this. It 
will slow down writes quite significantly, due to network latency (async 
is more bandwidth-hungry, sync more latency so) and the added complexity 
(distributed locking etc), which will also increase network traffic.
    There are a few other options though. One is the semi-sync 
replication as documented here:
http://code.google.com/p/google-mysql-tools/wiki/SemiSyncReplicationDesign
another is using the replication slave look-ahead,  which will speed up 
replication (Google for this guy).
    The Master-Master replication setup will of course still do you some 
good. It will allow you to catch replication conflicts and handle them, 
instead of the replication system stopping or some other ill effect of 
the "blind" replication as in "normal" MySQL replication. This said, CGE 
is mainly a Cluster release, even though other storage engines are part 
of it. For this reason, if I was in your shoes, I'd go with MySQL 
replication and doing what I can to speed up replication performance, 
the relay log lookahead being particularily interesting, as it does not 
require any changes to the MySQL core.

Cheers
/Karlsson
Michael Varlik wrote:
> Hi,
>
> I have several sites which are connected via wide area networks.
> Each of these sites has one MySQL database which serves it's local
> clients. But the data from one single site has to be available to
> all other sides. If possible in realtime.
> First, I thought about setting up a cluster with data nodes spread
> across all sites but this doesn't seem to be a good choice, isn't it?
> Now I've read about master-master replication of MySQL Cluster CGE.
>
> What exactly is master-master replication and can it be a suitable
> technology to replicate data between several sites close to realtime?
>
> Many thanks in advance for your sugestions.
> Best regards,
> Michael
>   


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