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Migrating from Cassandra to MongoDB or What Can be Learned Here?

The story here is simple: hit a crazy ☞ bug in Cassandra (remember all these tools are really young), they needed their data before a fix was available (keep in mind that some are using these NoSQL solutions in production), migration to MongoDB (while in production, you’ll do whatever it takes to minimize downtime):

Data migration

At some point we started to have some stability issues with Cassandra. All nodes would go into an infinite loop, running GC and trying to compact the data files – occasionally falling off the cluster. We were unable to solve the problem, except that restarting and then compacting a node usually settled it down for a while. Other people had reported similar problems. Last couple of weeks our Cassandra nodes always ate all the resources they were given, slowing down Flowdock.

Anyways, I think there’s a lesson here: all NoSQL databases should start providing a data export tool.