public class SweepJobNodeTracker
Tracker on the sweep tool node in zookeeper.
The sweep tool node is an ephemeral one, when the process dies this node is deleted,
at that time MR might be still running, and if another sweep job is started, two MR
for the same column family will run at the same time.
This tracker watches this ephemeral node, if it's gone or it's not created by the
sweep job that owns the current MR, the current process will be aborted.
public void start()
Registers the watcher on the sweep job node.
If there's no such a sweep job node, or it's not created by the sweep job that
owns the current MR, the current process will be aborted.
This assumes the table lock uses the Zookeeper. It's a workaround and only used
in the sweep tool, and the sweep tool will be removed after the mob file compaction