Performance between 'Values API' and 'Serde Compatible API'.

[ZhaiMo15]

I noticed that simd-json offers two main entry points for usage: 'Values API' and 'Serde Compatible API'. I ran benches/parse.rs to test the performance. I added code below to test simd_json::serde::from_slice:

fn simd_from_slice(data: &mut [u8]) {
    let _: serde_json::Value = simd_json::serde::from_slice(data).unwrap();
}

group.bench_with_input("simd_json::serde::from_slice", &vec, |b, data| {
    b.iter_batched(
        || data.clone(),
        |mut bytes| simd_from_slice(&mut bytes),
        BatchSize::SmallInput,
    )
});

Here's the result:	Throughput(MiB/s)	simd_json:: to_borrowed_value	simd_json:: to_borrowed_value_with_buffers	simd_json:: to_owned_value	simd_json:: serde::from_slice	serde_json:: from_slice
apache_builds	378.61	323.86	170.99	164.81	140.08
event_stacktrace_10kb	983.51	1070.9	762.83	709.25	501.10
github_events	455.06	442.80	226.45	178.68	141.91
canada	142.38	164.17	146.48	114.10	152.69
citm_catalog	312.69	340.59	234.10	237.55	225.40
log	403.55	467.40	196.92	155.88	119.01
twitter	367.24	372.41	207.64	156.72	120.17

The 'Values API' is mostly better than serde except canada(146.48 vs 152.69). However, the performance of 'Serde Compatible API' seems not that good, the result of canada cannot be acceptable(114.10 vs 152.69). I'd like to use simdjson to increase the performance, so it's better to use 'Values API'? And if my data is similar to canada, it's better not to use simdjson?

[Licenser]

Hi,

sorry for the late reply I'm just finishing some vacationing and was mostly away from the computer.

That makes a good bit of sense, the serde mapping code is quite complex and by that expensive to execute - irespective of the decoder (serde-json, simd-json, serde-yaml ... etc).

By contrast the value API is kept as simple as possible so the overhead is just lower. In some cases the extra cost of allowing abritary values is less then the extra cost of serde.

There is a 3rd api, the simd-json-derive api that allows to decide directly into structs w/o the value API, that will be faster still but is less flexible.

Last but not least, I want to point out that this isn't serde being bad, or not well written. serde is made to allow nearly arbritary format translations and is extremely powerful that way - it does this extremely well, but such power usually comes at a cost. the simd-json-derive macros are extremly specific so can take a lot of shortcuts serde simply can't that's where the performance benefit can be gained.

[PSeitz]

I implemented the ValueBuilder trait for serde_json_borrow::Value. In this bench it is slightly slower than the simd_json serde variant in most benches. I think it should slightly faster than BorrowedValue, as the datastructures are simpler. I didn't profile, but could be related to missing inlines, as this is cross-crates.

There's also a dependency to halfbrown::Hashmap on the simd_json::value::deserialize API. It would be good to reexport or switch to something more generic like an Iterator.

The branch is here https://github.com/PSeitz/serde_json_borrow/tree/simd_json_value_builder.

Library	Dataset	Avg Speed
serde_json	flat_json	137.96 MiB/s
serde_json_borrow	flat_json	208.32 MiB/s
simd_serde_json_borrow	flat_json	122.62 MiB/s
simd_serde_json_borrow_value_builder	flat_json	118.30 MiB/s
simd_json_BorrowedValue	flat_json	134.90 MiB/s
serde_json	hdfs	287.32 MiB/s
serde_json_borrow	hdfs	389.00 MiB/s
simd_serde_json_borrow	hdfs	263.32 MiB/s
simd_serde_json_borrow_value_builder	hdfs	253.54 MiB/s
simd_json_BorrowedValue	hdfs	288.18 MiB/s
serde_json	hdfs_with_array	200.19 MiB/s
serde_json_borrow	hdfs_with_array	283.97 MiB/s
simd_serde_json_borrow	hdfs_with_array	163.14 MiB/s
simd_serde_json_borrow_value_builder	hdfs_with_array	192.23 MiB/s
simd_json_BorrowedValue	hdfs_with_array	209.96 MiB/s
serde_json	wiki	446.33 MiB/s
serde_json_borrow	wiki	488.47 MiB/s
simd_serde_json_borrow	wiki	555.05 MiB/s
simd_serde_json_borrow_value_builder	wiki	544.57 MiB/s
simd_json_BorrowedValue	wiki	582.90 MiB/s
serde_json	gh-archive	175.92 MiB/s
serde_json_borrow	gh-archive	362.67 MiB/s
simd_serde_json_borrow	gh-archive	343.65 MiB/s
simd_serde_json_borrow_value_builder	gh-archive	328.93 MiB/s
simd_json_BorrowedValue	gh-archive	397.70 MiB/s

[Licenser]

This is really awesome @PSeitz !