Is Rails 4 going to render JSON as a stream by default?

I have some pretty big data to be encoded to JSON in my application and it would be faster if rendering my data as JSON could be done with a stream response.

So, if the network is the bottleneck, the clients wouldn't notice some seconds of delay before starting to receive the JSON response that is required for the server to process JSON encoding before starting to send it to the client...

Are you considering any kind of optimization like this for Rails 4?

As far as I know there is no plans to make it the default, but nothing stops you from using ActionController::Live to stream JSON as soon as you generate it.

It is not as simple as one might think.

It requires streaming support by the JSON library itself since the

point is to start streaming the output before the JSON encoding is

You should be able to pass the output streaming buffer object to the

JSON formatter library. For instance, suppose you have something
like this object:

{keyA: 'a value', keyB: anotherObject}

As the JSON formatter library reads this object, it would start with

some key, right? Suppose it starts with “keyA”. So the browser would
get a chunk like this:

{"keyA": "a value"

Then it would get another chunk like:

, "keyB":

And it goes on until all object processing is finished. Of course I

just simplified the idea. What would really give a boost in my case
would be the ability to use multiple cores to format the JSON by
splitting the task in multiple threads (or processes depending on
what Ruby implementation the library is targetting to).

Since JSON became the de facto format to exchange data between

servers and browsers any effort to speed up its encoding/decoding
(specially encoding) would be of much value to any web framework.

I'd love to see some performance improvements over JSON responses.

Unfortunately I don't have time this year to work on such

improvements since I’m currently with a very tight deadline that has
been already missed due to Sandy’s hurricane that affected our
collocation service provider in NYC.

Please let me know if I wasn't clear enough of what performance

improvements I’m suggesting to Rails 4 with regards to JSON



I’m aware that you need to have the library support for that, but this is not a rails concern. Rails depends on multi_json (well, technically Active Support depends on it) and you can choose any library you want to render JSON with rails. If you need this kind of feature, you should rather talk with maintainers of one of the JSON libraries out there.

Yajl is capable of doing it. So hacking together Yajl and ActionController::Live might give you streaming json as it is produced.

Robert Pankowecki

Thank you, Robert, I’ll give it a try once Rails 4 is released.