private void countDownLatch(Map<String, CountDownLatch> countDownLatchMap, String partitionName) {
    CountDownLatch latch = countDownLatchMap.get(partitionName);
    if (latch == null) {
      throw new IllegalStateException("No countdown latch is found for partition " + partitionName);
    } else {
      latch.countDown();
    }
  }
Count down the latch associated with given partition
@param countDownLatchMap the map in which the latch is specified for given partition.
@param partitionName the partition whose corresponding latch needs to count down.
ambry-clustermap/src/main/java/com/github/ambry/clustermap/AmbryReplicaSyncUpManager.java