When a client adds a cache directive, we assign it a unique ID and return that ID to the client. If multiple clients add a cache directive for the same path, then we return the same ID. If one client then removes the cache entry for that ID, then it is removed for all clients. Then, when this change becomes visible in subsequent cache reports, the datanodes may munlock the block before the other clients are done with it.
- relates to
HDFS-4949 Centralized cache management in HDFS