void decStateTransitionMetric(String partitionName, ReplicaState from, ReplicaState to) {
    String metricName = String.format(stateTransitionMetricTemplate, partitionName, from.toString(), to.toString());
    if (partitionTransitionToCount.containsKey(metricName)) {
      partitionTransitionToCount.get(metricName).dec();
    }
  }
Decrements the metric for given partition's state transition
@param partitionName partition name
@param from begin name
@param to end state
ambry-clustermap/src/main/java/com/github/ambry/clustermap/HelixParticipantMetrics.java