JobHistory cache issue
https://issues.apache.org/jira/browse/MAPREDUCE-6436
可能导致打印的日志太多影响性能 Job history server scans can become blocked on a single, slow entry
https://issues.apache.org/jira/browse/MAPREDUCE-6797 High contention on scanning of user directory under immediate_done in Job History Server
https://issues.apache.org/jira/browse/MAPREDUCE-6684