int getCompactionThreadCount() {
    int count = 0;
    for (DiskManager diskManager : diskToDiskManager.values()) {
      if (diskManager.isCompactionExecutorRunning()) {
        count++;
      }
    }
    return count;
  }
@return the number of compaction threads running.
ambry-store/src/main/java/com/github/ambry/store/StorageManager.java