rkyv VS unsafe-code-guidelines

And before you ask: This only provides partial zero-copy support in strings and byte arrays like serde. But it's not like rkyv which constructs validated references into the data.

Regarding JSON, what kind of other implementation do you have in mind? I've seen e.g. `rkyv` which looks really neat (https://github.com/rkyv/rkyv/issues/85). So far `serde_json` is providing a clean surface API but maybe there's best solution?

Thank you for your concern. I've done plenty of projects that go beyond a "Hello World" such as a GPU accelerated password cracker. I am starting soon a C++/Rust job. I already contributed to codebases I didn't write.

rkyv is awesome because it supports full zero-copy deserialization. You can serialize your HashMap to a file. Later you can directly use the HashMap from the file without creating and populating a new HashMap in memory (rkyv directly indexes into the raw bytes). For even faster access times you can even mmap the file.

I had the same problem when trying to deserialize a big struct with rkyv: see rkyv#277.

Any chance of working with zero-copy deserialization frameworks? like https://github.com/rkyv/rkyv or capnproto

Hi, you seem to know a bit about Sanakirja!

It stores 4kb blobs, right? Does Pijul first parses the data (copying it to other allocations), or uses the data as is? I mean, there are some libraries like cap'n'proto[0] and rkyv[1] that can directly use the file contents as an in-memory data structure, I was wondering if Pijul did anything like that.

I mean, is this btree page [2] stored exactly like this on disk, and does Pijul exploits that to avoid further copying data?

(I guess there's a trouble with compression there: to decompress you really need to write in another buffer)

Also, is the I/O done with something that prevent userspace copies like mmap or io_uring, or does it eventually calls read() to copy the data to its own buffer?

I want to build something like Sanakirja, but with those features, so I'm wondering if there's any overlap.

[0] https://github.com/capnproto/capnproto-rust

[1] https://github.com/rkyv/rkyv

[2] https://docs.rs/sanakirja-core/latest/sanakirja_core/btree/p...

I think https://github.com/rkyv/rkyv does this. Also capnproto like was mentioned here, and perhaps https://docs.rs/zerocopy/0.6.1/zerocopy/index.html too

It's been two months since the last major rkyv release, and three months since the last major feature release. After all that time, I'm proud to announce that rkyv 0.7 is finally out!

After roughly two months of work, rkyv 0.5 is finally out!

Useful context on the Rust side is this issue [1]. It sounds like some of the author's concerns are addressed already.

[1]: https://github.com/rust-lang/unsafe-code-guidelines/issues/4...

Is this captured by one of the known soundness conflicts? If not then should consider adding it to the list.

There are some competing proposals for different memory models. Stacked borrows is the current proposal, but there are more work in the approproate WG.

Thank you /u/RalfJung for bringing formal methods to Rust, both through models like Stacked Borrows, by developing miri, and by working on unsafe-code-guidelines which aims to specify exactly what is and isn't allowed in unsafe code (surprisingly, it's an open question as 2023!)

You could imagine some way to make this safe for example automatically convert &'short &'long mut T to &'short &'short T, but it's non-trivial to prove they are safe at all, not to mention ensuring this is correctly implemented in the compiler. If you're interested there's also a discussion on whether the opposite (& & T to & &mut T) is sound here.

Agreed! MIRI is so good, it still feels like magic to me. It also comforts me that the Rust team takes improving unsafe semantics seriously, with the past Unsafe Code Guidelines WG and today's operational semantics team (t-opsem).

I think there are some aspects of this rule that are still undecided. See for example:

- https://github.com/rust-lang/unsafe-code-guidelines/issues/8...

- https://github.com/rust-lang/miri/issues/2732

C is much better specified than unsafe Rust. Some things are just not worked out yet in Rust. This may sometimes even bite very experienced devs, such as this issue with Box's aliasing semantics, which tripped up the author of left-right.