Statistical information exposed by the Hadoop daemons is Metrics. Hadoop framework uses it for monitoring, performance tuning and debug.
By default, there are many metrics available. Thus, they are very useful for troubleshooting.
Hadoop framework use hadoop-metrics.properties for ‘Performance Reporting’ purpose. It also controls the reporting for Hadoop. The API provides an abstraction so we can implement on top of a variety of metrics client libraries. The choice of client library is a configuration option. And different modules within the same application can use different metrics implementation libraries. This file is present inside /etc/hadoop.