@Override
    public void onPartitionBecomeLeaderFromStandby(String partitionName) {
      logger.info("Partition state change notification from Standby to Leader received for partition {}",
          partitionName);
    }
{@link PartitionStateChangeListener} to capture changes in partition state.
ambry-server/src/main/java/com/github/ambry/server/StatsManager.java