RocksDB 4.9 发布了，RocksDB 是一个来自 facebook 的可嵌入式的支持持久化的 key-value 存储系统，也可作为 C/S 模式下的存储数据库，但主要目的还是嵌入式。RocksDB 基于 LevelDB 构建。关于 RocksDB 的性能说明。
改进日志：
Public API 更新：
Add bottommost_compression option, This option can be used to set a specific compression algorithm for the bottommost level (Last level containing files in the DB).
Introduce CompactionJobInfo::compression, This field state the compression algorithm used to generate the output files of the compaction.
Deprecate BlockBaseTableOptions.hash_index_allow_collision=false
Deprecate options builder (GetOptions()).
新特性
Introduce NewSimCache() in rocksdb/utilities/sim_cache.h. This function creates a block cache that is able to give simulation results (mainly hit rate) of simulating block behavior with a configurable cache size.
详情：https://github.com/facebook/rocksdb/blob/master/HISTORY.md