Getting the datanode reports is an expensive operation and can be executed very frequently by the UI and watchdogs.
To reduce this load, this information is cached in the Router.
This cached information expires after some time (configurable).
- relates to
HDFS-13364 RBF: Support NamenodeProtocol in the Router
HDFS-15432 RBF: Move cache datanode reports from NamenodeBeanMetrics to RouterRpcServer