simd-json
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Rust port of simdjson
SIMD Json for Rust
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Rust port of extremely fast simdjson JSON parser with serde compatibility.
readme (for real!)
simdjson version
Currently tracking version 0.2.x of simdjson upstream (work in progress, feedback welcome!).
CPU target
To be able to take advantage of simd-json
your system needs to be SIMD capable. This means that it needs to compile with native cpu support and the given features. This also requires that projects using simd-json
also need to be configured with native cpu support. Look at The cargo config in this repository to get an example of how to configure this in your project.
simd-json
supports AVX2, SSE4.2 and NEON.
Unless the allow-non-simd
feature is passed to your simd-json
dependency in your Cargo.toml
simd-json
will fail to compile, this is to prevent unexpected slowness in fallback mode that can be hard to understand and hard to debug.
allocator
For best performance we highly suggest using mimalloc or jemalloc instead of the system allocator used by default. Another recent allocator that works well ( but we have yet to test in production a setting ) is snmalloc.
serde
simd-json
is compatible with serde and serde-json
. The Value types provided implement serializers and deserializers. In addition to that simd-json
implements the Deserializer
trait for the parser so it can deserialize anything that implements the serde Deserialize
trait. Note, that serde provides both a Deserializer
and a Deserialize
trait.
That said the serde support is contained in the serde_impl
feature which is part of the default feature set of simd-json
, but it can be disabled.
known-key
The known-key
feature changes the hash mechanism for the DOM representation of the underlying JSON object, from ahash
to fxhash
. The ahash
hasher is faster at hashing and provides protection against DOS attacks by forcing multiple keys into a single hashing bucket. The fxhash
hasher on the other hand allows for repeatable hashing results, which in turn allows memoizing hashes for well known keys and saving time on lookups. In workloads that are heavy at accessing some well known keys this can be a performance advantage.
The known-key
feature is optional and disabled by default and should be explicitly configured.
serializing
simd-json
is not capable of serializing JSON data as there would be very little gain in re-implementing it. For serialization, we typically rely on serde-json
.
For DOM values we provide convience methods for serialization.
For struct values we defer to external serde-compatible serialization mechanisms.
unsafe
simd-json
uses a lot of unsafe code.
There are a few reasons for this:
- SIMD intrinsics are inherently unsafe. These uses of unsafe are inescapable in a library such as
simd-json
. - We work around some performance bottlenecks imposed by safe rust. These are avoidable, but at a cost to performance. This is a more considered path in
simd-json
.
simd-json
goes through extra scrutiny for unsafe code. These steps are:
- Unit tests - to test 'the obvious' cases, edge cases, and regression cases
- Structural constructive property based testing - We generate random valid JSON objects to exercise the full
simd-json
codebase stochastically. Floats are currently excluded since slighty different parsing algorithms lead to slighty different results here. In short "is simd-json correct". - Data-oriented property based testing of string-like data - to assert that sequences of legal printable characters don't panic or crash the parser (they might and often error so - they are not valid json!)
- Destructive Property based testing - make sure that no illegal byte sequences crash the parser in any way
- Fuzzing (using American Fuzzy Lop - afl) - fuzz based on upstream simd pass/fail cases
This doesn't ensure complete safety nor is at a bullet proof guarantee, but it does go a long way to asserting that the library is production quality and fit for purpose for practical industrial applications.
Other interesting things
There are also bindings for upstream simdjson
available here
License
simd-json itself is licensed under either of
- Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
- MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT) at your option.
However it ports a lot of code from simdjson so their work and copyright on that should be respected along side.
The serde integration is based on their example and serde-json
so again, their copyright should as well be respected.