@Override
  public Status read(String table, String key, Set<String> fields, Map<String, ByteIterator> result) {
    try {
      byte[] value = db.get(key.getBytes());
      Map<String, ByteIterator> deserialized = deserialize(value);
      result.putAll(deserialized);
    } catch (RocksDBException e) {
      System.out.format("[ERROR] caught the unexpceted exception -- %s\n", e);
      return Status.ERROR;
    }
    return Status.OK;
  }

  @Override
  public Status scan(String table, String startkey, int recordcount,
                  Set<String> fields, Vector<HashMap<String, ByteIterator>> result) {
    System.out.println("Scan called! NOP for now");
    return Status.OK;
  }

  @Override
  public Status update(String table, String key, Map<String, ByteIterator> values) {
    try {
      byte[] serialized = serialize(values);
      db.put(key.getBytes(), serialized);
    } catch (RocksDBException e) {
      System.out.format("[ERROR] caught the unexpceted exception -- %s\n", e);
      return Status.ERROR;
    }
    return Status.OK;

 @Override
  public Status read(String table, String key, Set<String> fields, Map<String, ByteIterator> result) {
    try {
      byte[] value = db.get(key.getBytes());
      Map<String, ByteIterator> deserialized = deserialize(value);
      result.putAll(deserialized);
    } catch (RocksDBException e) {
      System.out.format("[ERROR] caught the unexpceted exception -- %s\n", e);
      return Status.ERROR;
    }
    return Status.OK;
  }

  @Override
  public Status scan(String table, String startkey, int recordcount,
                  Set<String> fields, Vector<HashMap<String, ByteIterator>> result) {
    System.out.println("Scan called! NOP for now");
    return Status.OK;
  }

  @Override
  public Status update(String table, String key, Map<String, ByteIterator> values) {
    try {
      byte[] serialized = serialize(values);
      db.put(key.getBytes(), serialized);
    } catch (RocksDBException e) {
      System.out.format("[ERROR] caught the unexpceted exception -- %s\n", e);
      return Status.ERROR;
    }
    return Status.OK;

刚写了两个数据库增删改查的接口， 为什么要用 ByteIterator？有什么好处？什么场景下用？
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