[spray-json] preserving field order for JSON objects

[Ian Forsey]

Hi,

We were curious about the reasoning behind preserving field order in JSON objects in spray-json, since the JSON spec does not require any ordering:

https://github.com/spray/spray-json/blob/master/src/main/scala/spray/json/JsValue.scala#L56

We ran a load test on our application using a Map rather than a ListMap here and saw a big reduction in our memory allocations. About 40% - 100gb -> 60gb.

Would you accept a PR that uses a simple Map here? Maybe behind a configuration option as to not break backwards compatibility.

Thanks

Ian

[Mathias Doenitz]

Ian,

> Would you accept a PR that uses a simple Map here? Maybe behind a configuration option as to not break backwards compatibility.

Yes, sure, thanks!

Cheers,
Mathias

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[nic]

It would be nice to be able to write objects with a consistent field order, or at least the same order just when the object is the same, so the string represenation of an object is always the same, and then you can just compare strings to know weather two objects are different. This is useful for map-reduce...    ++nic

[Mathias Doenitz]

Nic,

check out the discussion in this ticket: https://github.com/spray/spray-json/issues/119
on the topic.

Cheers,
Mathias

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