Performance comparison with other existing libraries in README.md

[StefanoD]

This would be interesting for many developers and a strong argument to use this library, respectively rust instead of another language.

In the comparison the version number of the respective lib should be indicated.
Especially a comparison with serd is interesting.
https://github.com/serde-rs/serde

[dtolnay]

This would be interesting, although my impression is that this library optimizes for easy API and low learning curve over performance.

We have some benchmarks of HashMap and Vec deserialization with varying types and varying sizes using both Serde and RustcDecodable at bench_map.rs and bench_vec.rs. I would be curious to see the same benchmarks against json-rust. EDIT: never mind, these are benchmarks of core Serde not serde_json.

[dtolnay]

@StefanoD I tried a benchmark of deserializing this Log object. My code is at dtolnay/serde-json@2acc39d.

Library	Output	Time	Throughput
serde	Log	5,135 ns/iter (+/- 73)	117 MB/s
serde	serde_json::Value	8,455 ns/iter (+/- 103)	71 MB/s
rustc-serialize	json::Json	12,287 ns/iter (+/- 53)	49 MB/s
json-rust	json::JsonValue	14,548 ns/iter (+/- 1,094)	41 MB/s
rustc-serialize	Log	17,170 ns/iter (+/- 219)	35 MB/s

Notice that Serde takes advantage of knowing the shape of the output. It is significantly faster to deserialize to Log compared to the enum, so json-rust has a handicap there. (That said, the opposite is true for rustc-serialize which deserializes Log by going to the Json enum first.)

[StefanoD]

@dtolnay Thank you very much. This is very impressive!
BTW: Did I note correctly, that there is json-rust to Log missing?
Could you publish similar benchmarks on your serd github webpage and compare i. e. serd with popular JSON libs?

[dtolnay]

There is a json-rust to Log missing because json-rust does not support that.

I filed serde-rs/json#82 to add benchmarks to the serde_json readme.

[StefanoD]

Thank you, very much!

[maciejhirsz]

@dtolnay This is pretty awesome, it's good to see I've room for improvement, and it's good to know that I'm not terribly far behind to begin with and things are usable as they are. I reckon my string parsing can be much better, since I just hacked in proper escaped characters handling yesterday.

[maciejhirsz]

@dtolnay Waited a bit with this issue till I got time to look into performance. I did take a clue from Serde and reworked things to use bytes instead of characters, tests results on the same JSON as above on my machine as of 0.7.1:

Library	Parsing	Serializing
Serde	10,316 ns/iter (+/- 797) = 62 MB/s	3,341 ns/iter (+/- 298) = 192 MB/s
json-rust	10,587 ns/iter (+/- 642) = 60 MB/s	2,685 ns/iter (+/- 314) = 239 MB/s
rustc-serialize	15,995 ns/iter (+/- 1,179) = 40 MB/s	5,022 ns/iter (+/- 278) = 128 MB/s

Codez

I haven't put in benches with the Log struct, there is a lot of boilerplate there, I might just copy over the file tomorrow. I reckon it makes sense to inform people the about pros and cons of serializing to generic values vs struct, so before I push anything to README I'd rather have a complete breakdown.

Sidenote: this is probably the most nerdy fun I've had in a long while :).

[StefanoD]

Oh, please don't close this! :)
A language comparison would be interesting, also. At least a comparison with the popular Java Lib "Jackson" would be nice.
And don't forget to add the version number of the lib as performance improvements can always be accomplished as you experienced yourself. ;)

[maciejhirsz]

Funny that you mention Jackson, since Jackson was one of the main inspirations for this (in the sense of: "oh dear, I really don't want to deal with that again").

I'll add versions. Currently the benchmarks are running via cargo bench on nightly, to benchmark Java things might get a bit more complicated, but I'll look into that.