public void access(long accessTime) {
    this.accessTime = accessTime;
    if (this.priority == BlockPriority.SINGLE) {
      this.priority = BlockPriority.MULTI;
    }
  }
Block has been accessed.
@param accessTime Last access; this is actually a incremented sequence number rather than an
                  actual time.
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/LruCachedBlock.java