Can multiple RocksDB instances share and read from the same key-range?

Question

Past answers on Stack Overflow suggest that the single threaded nature of RocksDB means the answer is no, but official FB documentation has pages like this http://rocksdb.org/blog/2021/05/27/rocksdb-secondary-cache.html where multiple instances seem to be sharing a cache.

1)Are these instances using the same key range?

2. If so, how are updates being communicated from one DB instance to another? As far as I know RocksDB doesn't have any interDB communication?

Answer 1

1. DB instances do not share key range.

Just FYI. one process can have multiple RocksDB instances, each instance can have multiple column-families. They do not share user-data. Internally, column-families in one instance share WAL (write ahead log), manifest (tracking db information), option file. DB instances in one process share the same Env, threadpool, timer, cache.