private long getOldestWalTimestamp() {
    long oldestWalTimestamp = Long.MAX_VALUE;
    for (Map.Entry<String, PriorityBlockingQueue<Path>> entry : queues.entrySet()) {
      PriorityBlockingQueue<Path> queue = entry.getValue();
      Path path = queue.peek();
      // Can path ever be null ?
      if (path != null) {
        oldestWalTimestamp =
          Math.min(oldestWalTimestamp, AbstractFSWALProvider.WALStartTimeComparator.getTS(path));
      }
    }
    return oldestWalTimestamp;
  }
Remove all the elements from the queue corresponding to walGroupId
@param walGroupId walGroupId
hbase-server/src/main/java/org/apache/hadoop/hbase/replication/regionserver/ReplicationSourceLogQueue.java