Protocol buffers handling very large String message?

Question

Hi all, I was finally able to write protocol buffers code over REST and did some comparison with XStream which we are currently uses. Everything seems great, only stumble with one thing.

We have very large messages in one particular attributes, say something like this

message Data {
   optional string datavalue=1;
}

Datavalue above are extremely huge text messages. Size is 512kb - 5 Mb.

Protocol buffers deserialize just fine, with superb performance comparing to XStream. However, I notice when I send this message to wire (via REST), it took longer to get response. Always twice longer than XStream. I am thinking this might come from serializing time.

From google documents, it says Protocol buffers is not designed to handle very large messages, although it can handle very large data set.

I was wondering if anyone has some opinion or maybe solution from my case above?

Thanks