The HMaster has two RPC handler pools, one for priority tasks, the other for regular ones. The regular ones see activity regularly and are represented by the section "B.defaultRpcServer" and you'll find that these continually process client or RS calls made to them.
The priority ones, on the other hand, only see limited activity relating to certain specific work, and will mostly be idle depending on your cluster's situation. It is normal to see a very large "Waiting since" value on the priority handlers, as they are used only in special situations.
Some more bits for your information:
- "Waiting for a call" means that the thread is idle and is waiting for some work to flow in.
- The "queue=X" value here is a queue identifier associated to the specific handler thread ID (there are multiple parallel queues that the handlers feed themselves from) and not the size of queue.
These waiting statuses on the HMaster UI only appear if you switch the Tasks tabs to show all monitored tasks or all RPC tasks regardless of state. If you're interested in finding actual calls, use the "Show Active RPC Calls" tab under it instead, and you may be able to catch some of the calls that regularly come in.
