* We have refactored our system of stalling writes. Any stall-related statistics' meanings are changed. Instead of per-write stall counts, we now count stalls per-epoch, where epochs are periods between flushes and compactions. You'll find more information in our Tuning Perf Guide once we release RocksDB 3.6.
* When disableDataSync=true, we no longer sync the MANIFEST file.
* Add identity_as_first_hash property to CuckooTable. SST file needs to be rebuilt to be opened by reader properly.
### Public API changes
* Change target_file_size_base type to uint64_t from int.
* Remove allow_thread_local. This feature was proved to be stable, so we are turning it always-on.