[erlang-questions] MNesia replication in ec2

Ryan Brown ryankbrown@REDACTED
Wed Apr 9 20:04:41 CEST 2014

Thanks Geoff. That is pretty-much what I thought. Wasn't sure if anybody
had experience using something like Ulf Wiger's unsplit (
https://github.com/uwiger/unsplit) to handle these events in this type of
environment or not. But, ultimately, I think an external solution like Riak
will be the best option as well.

Thanks again.


On Tue, Apr 8, 2014 at 3:20 PM, Geoff Cant <nem@REDACTED> wrote:

> On EC2 you will inevitably experience network conditions that will cause
> mnesia to decide that it is partitioned. There is no way to perform an
> online recovery from a partition event[1] without stopping and restarting
> the mnesia application. Unless you design your app to go into a degraded
> operation mode where all mnesia operations are either avoided or errors
> caught, then you'll experience a lot of trouble with it.
> Additionally, mnesia recovers by copying the entire table from another
> node - this is fine(ish) for small datasets, but if your dataset grows over
> time, you'll eventually find yourself unable to bring new/recovering nodes
> online quickly which blows up your Mean Time To Repair.
> I think multi-data-center Riak sounds like a better fit for multi-region
> ec2 work honestly, but I have not personally used Riak in that scenario so
> I defer to others.
> -Geoff
> [1] Pretty sure that's still true?
> On 2014-04-08, at 14:14 , Ryan Brown <ryankbrown@REDACTED> wrote:
> > We are in the process of laying the groundwork for deploying our
> application to ec2.  We currently depend upon mnesia replication for a
> small amount of shared metadata in our datacenter. I've read a number of
> posts/articles that have given me pause when thinking about how mnesia will
> work across AZs, regions in ec2. Primarily regarding network partitioning.
> We are currently considering removing our use of mnesia and pushing the
> small amount of data we replicate to shared store (possibly Riak).
> >
> > Does anybody out there have experience with this or guidance?
> >
> > --
> > -rb

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