Investigate possibility of using RocksDB as backend

[siepkes]

Wren:DS has a plugable storage backend. Currently it primarily uses Berkeley DB Java edition as storage backend. At some point it also supported PDE however that didn't workout well so support was marked deprecated. PDE support was added due to ForgeRock's concerns about the licensing of Berkeley DB. However soon after PDE support was released the licensing of Berkeley DB was changed to a license which no longer posed a problem for ForgeRock.

While Berkeley DB was long the go to embedded storage backend new challengers have emerged. One of these is RocksDB. RocksDB was / is developed by Facebook and is based on research by Google (LevelDB).

RocksDB is supposedly, very, very fast. I think it would be interesting to do some research to see if A) RocksDB could be used as a backend for Wren:DS and B) If so, how much performance gain would that give us.