@Override
  public void stop(CoprocessorEnvironment env) throws IOException {
    // since meta region can move around, clear stale metrics when stop.
    for (String metric : metrics) {
      registry.remove(metric);
    }
  }
Get regionId from Ops such as: get, put, delete.
@param op such as get, put or delete.
hbase-server/src/main/java/org/apache/hadoop/hbase/coprocessor/MetaTableMetrics.java