[HDFS-10187] Add a "list" refresh handler to list all registered refresh identifiers/handlers

• Type: New Feature
• Status: Patch Available
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 2.7.2
• Labels: commandline supportability
• Release Note: Added a command 'hdfs dfs admin -refresh <nn:ipc_port> list' to list all registered refresh identifiers and handlers.
• Assignee: Wei-Chiu Chuang
• Reporter: Wei-Chiu Chuang
• Created: 21/Mar/16 14:48
• Updated: 21/Mar/16 19:57

Description

HADOOP-10376 added a new feature to register handlers for refreshing daemon configurations, because name node properties can be reconfigured without restarting the daemon. This can be a very useful generic interface, but so far no real handlers have been registered using this interface. I added a new 'list' handler to list all registered handlers. My plan is to add more handlers in the future using this interface.

Another minor fix is return a more explicit error message to the client if a handler is not registered. (It is currently logged at namenode side, but client side only gets a "Failed to get response." message without knowing why)

Issue Links

• relates to: HADOOP-10376 Refactor refresh*Protocols into a single generic refreshConfigProtocol