TL;DR On writes RocksDB is first, then PerconaFT, then WiredTiger. Interesting results. Last months I saw the production use of MongoDB with RocksDB engine onl

TL;DR On writes RocksDB is first, then PerconaFT, then WiredTiger. Interesting results. Last months I saw the production use of MongoDB with RocksDB engine only once. Do you use engines other than WiredTiger (or mmapv1) and what were your reasons to do it?