[hendzen]

How much do you think RocksDB/LevelDB performance is impacted by the use of relatively coarse-grained locking? Another LevelDB fork, HyperLevelDB [1] implemented a fine grained scheme with performance benefits. Disclaimer: I am working on a (unreleased) fork of LevelDB that uses hardware transactional memory for synchronization using the new TSX-NI instructions present on Haswell processors.

[1] - http://hyperdex.org/performance/leveldb/

[dhruba_b]

This is an excellent question. RocksDB has a lock per shard that is used to protect incrementing/decrementing refcounts on critical metaddata structures for writes. It is never held during actual IO to storage. We have been able to saturate a flash device for a pure-write workload when value size = 800 bytes without bottlenecking on this lock.