RocksDB started as a fork of LevelDB (Dean/Ghemawat). The performance imperatives have changed with the hardware, but NAND flash at that time had an asymmetry

RocksDB started as a fork of LevelDB (Dean/Ghemawat). The performance imperatives have changed with the hardware, but NAND flash at that time had an asymmetry between reads and writes in terms of the amount of data: once you were writing even one byte you had effectively paid for writing a whole block and were therefore incentivized to get your money’s worth and write to a “log”, which then would be “merged”, in some “structured” way, hence LSM. This is old news these days but it was quite the novelty at the time!