Erlang JSON libraries: serialization performance?

Question

There are a number of JSON libraries available for Erlang, and it's not clear to me which have the best performance characteristics (and, secondarily, ease of use), especially for erlang-to-json serialization.

My use case requires both JSON parsing and serialization, but the Erlang code will probably be producing at least two orders of magnitude more JSON output (i.e. serialization) than it will receive input.

For reference, the libraries I know of include the following (and there may be others I haven't found):

• mochijson
• mochijson2
• erlang-rfc4627
• eep0018

Answer 1

Hopefully this answer won't be ill-received, however:

I too looked into JSON parsing and serialization for a project. I had to process a lot of data in parallel, so Erlang sounded great! But a lot of that was dealing strings in the form of JSON data, and that's where things went sour.

As you probably know strings in Erlang are full fledged lists of characters. Unlike strings in most languages (a char is "about" a byte), each character in Erlang is represented by a whole 32-bit integer! So, already your strings are quite large.

Because it's a list, access to a given element of the string is O(N) instead of O(1) as you'd expected in an array of Chars. And, because strings are immutable in Erlang simple concatenation can end up being a very slow process. In the end I realized I was simply trying to use the wrong language.

In all likelihood you already know all of these things, but I felt it was useful to leave this as an answer for others who may at arrive at your post in the future.

Answer 2

I use rfc4627.erl (I stumbled upon it, and performance has not been an issue)

However, I do expect the different native erlang libraries to perform similarly well. They share ideas (as witnessed in the code comments). AFAIK mochijson and rfc4627 share the same source erlang format.

eep018 is C, and as it is striving to implement ... hrm ... eep-0018, the term_to_json native encoder that might be included in a future version of Erlang. Never tried it and doesn't seem actively maintained.

My final recommendation is go with mochiweb's mochijson(2). It is the de facto standard and actively maintained, used by, among others, CouchDB and Facebook.

As for choosing between mochijson and mochijson2, this might help you.

Answer 3

I've been using jsonerl lately. It's based on mochijson2 and is much more easy and intuitive to use.