MongoDB and RocksDB at Parse

MongoDB seems to have a bad rep on HN for its various shortcomings, and yet here FB/Parse seem to use it. Is the bad rep overrated? (Honest question)

What's the main use case for something like RocksDB ? Is it an out-of-process local caching engine (in-memory + unloads to disk if necessary) ? Or is it something different? Can it communicate between nodes? Why would I use it instead of a large dictionary in memory?

By the way, does anybody knows how Parse execute sandboxes javascript on the server ? I can't find an article on that matter.

&gt; The RocksDB engine developed by Facebook engineers is one of the fastest, most compact and write-optimized storage engines available.<p>Will it fix MongoDB&#x27;s data loss issues? I&#x27;m hoping that is what &quot;write-optimized&quot; is partly implying.

&quot;And we now have some exciting news to share: we are running MongoDB on RocksDB in production for some workloads and we’re seeing great results!&quot;<p>Some stats and a way to replicate would be nice here.