private static HashSet<Record> getDiffArea(Protocol protocol,
SocketChannel channel,
MismatchedRegion region)
throws Exception {
protocol.write(protocol.new RemoteDiffRequest(region), channel);
/* Check whether getting records on remote database is successful. */
Message message = protocol.read(channel);
if (message.getOp() == Protocol.ERROR) {
throw new LDiffRecordRequestException