@Deprecated
  public Scan setAsyncPrefetch(boolean asyncPrefetch) {
    this.asyncPrefetch = asyncPrefetch;
    return this;
  }
@deprecated Since 3.0.0, will be removed in 4.0.0. After building sync client upon async
            client, the implementation is always 'async prefetch', so this flag is useless now.
hbase-client/src/main/java/org/apache/hadoop/hbase/client/Scan.java