replication between datacenters

[dormando]

I mean you must have one logical master - multimaster fixes this to a
degree.

MogileFS in its current design _must_ only talk to one database or else
its locking scheme doesn't work. We use multimaster databases with
heartbeat to ensure all trackers are talking to a single database at any
time. Unfortunately (right now, anyway...) you can't have the trackers
just talk to the local database on each side.

-Dormando

Arnoud Vermeer wrote:
> You can use a mysql master-master setup to solve the problem of the
> single database. The trick is to use auto_increment_increment and
> auto_increment_offset so that you're auto_increment never gets screwed
> up. You can find really good documentation on onlamp.com
> <http://onlamp.com/> under advanced mysql replication*. I use the
> following settings: auto_increment_increment = 10
> auto_increment_offset = 1 on db10 and auto_increment_increment = 10
> auto_increment_offset = 2 on db20. This means you can scale to a
> replication ring of max 10 nodes.
> 
> You make one master at datacentre 1 and the other at datacentre 2. Let
> all the mogilefsd's connect to the local database or use heartbeat to
> switch them over.
> 
> *
> http://www.onlamp.com/pub/a/onlamp/2006/04/20/advanced-mysql-replication.html
> 
> Arnoud Vermeer
> 
> On Thu, May 22, 2008 at 1:37 AM, dormando <dormando at rydia.net
> <mailto:dormando at rydia.net>> wrote:
> 
>     MogileFS does replication between datacenters. There's still a
>     single database, but you can work with that a bit.
> 
>     In trunk there's code but no documentation for it. Basically you
>     configure network zones, then use a specific replication policy to
>     say how many copies you want in each network. The trackers will
>     return paths "local" to that client.
> 
>     There're no docs yet, but we run it in production and it works okay.
>     Fixes/updates coming, and it's not hard to set up if you want to
>     test it in a dev setup.
> 
>     Also, we got your mail three times :)
> 
>     -Dormando
> 
> 
>     William Francis wrote:
> 
>         * sorry if this comes through more than once. I sent a few hours ago
>         but it hasn't shown up on the list yet. gmail's IMAP has been weird
>         today :-/
> 
> 
>         We currently have mogilefs running quite satisfactorily for our
>         service and we're growing into a second datacenter initially for
>         disaster recovery but eventually load balancing as well.  After a
>         couple hours of searching and looking through CPAN I've noticed that
>         geographic replication seems to be something that has been discussed
>         several times in the past (here and elsewhere) but I've been
>         unable to
>         locate anything that suggests the best approach to take for our
>         situation.  Did I miss something or is this still in the realm
>         of 'gee
>         that'd be neat' but there's no generally accepted way to do it and
>         it's just been hacked together somehow each time by people who
>         need to
>         solve this problem?
> 
>         Any pointers greatly appreciated and thanks for something that works
>         beautifully!
> 
>         Will
> 
> 
>