Coherence out-of-the box provides resilience across the cluster. If you don’t run a cluster (ie: a single server) then loss of that machine will obviously lose data (if it’s only stored in memory). You can, like Terracotta configure Oracle’s Berkley DB to resolve this issue (and many others with Coherence), but as soon as you add more server instances (at run time without needing to go to a console or repartition your application), you automatically get resilience. If TC you have to configure all of this yourself. If you want to run in striped mode, you *have* to pay for the commercial edition (ie: no longer open source).

With Coherence (even standard edition), you can continue to scale out, at run-time, to hundreds or thousands of servers, without reconfiguring your application. You can also kill (like kill -( any server while it’s running and not lose information – this is without using Oracle BDB (or other storage).

Coherence is like RAID for an application, in the application teir. Terracotta is network attached storage, and it seems you have to treat it like a manually partitioned device. Both have their advantages and disadvantages, but in terms of reliability and scalability, I’ve not seen anything like it, no matter how much people try to compare other products to it (which is obviously nice).

– Brian

Thanks for your comment about Terracotta – just a question:

You’re saying “that all cache/clustered products have”, but I’m not aware of any specific single points of failure in Coherence using the standard configuration. Failure of any single cache node should not matter, considering there’s no central instance (like in a hub/spoke model) but rather all participating instances are peers and data always exist in more than one node at any point in time.

Did you have a certain failure mode in mind that includes Coherence as well as Terracotta?

Kindly,

/M

Nice bit. I should point out that Terracotta has the same single point of failure that all cache/clustered products have when setup using default configurations.

Regards,
Kirk