FAfanf2·Dec 29, 2024Submission
AHash: A fast non-cryptographic keyed hash for in-memory hashmaps
1 points · Open discussiontkaitchuck
aHash
Rust2021–2024
tkaitchuck / aHash
aHash
aHash is a non-cryptographic hashing algorithm that uses the AES hardware instruction
6Distinct people
9Mentions
0Explicit recommenders
1.4KGitHub stars
What to know before exploring
What it is
aHash is a non-cryptographic hashing algorithm that uses the AES hardware instruction
GitHub
Where it is used
No documented product use has been verified yet.
What people are saying
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This week on Hacker News
Nov 7–Nov 14 UTC · Direct repository links and separately labeled related project stories. Indexed through 11/14/2026, 3:56:07 PM UTC.
No direct repository links were found in the indexed HN discussions over the past seven days. Older discussions are available below.
Mentions over time
HN mentions by year9 dated mentions
Observed mentions: 2021-02-21 20:10:57 UTC to 2024-12-29 18:42:02 UTC.
Counts come from the repository’s dated source evidence. Index cutoff: 2026-11-02 08:16:59 UTC.
View mention counts and date ranges
| Period | Start (UTC) | End (exclusive, UTC) | Mentions | Submissions | Comments |
|---|---|---|---|---|---|
| 2021 | 2021-01-01 00:00:00 UTC | 2022-01-01 00:00:00 UTC | 3 | 1 | 2 |
| 2022 | 2022-01-01 00:00:00 UTC | 2023-01-01 00:00:00 UTC | 5 | 0 | 5 |
| 2023 | 2023-01-01 00:00:00 UTC | 2024-01-01 00:00:00 UTC | 0 | 0 | 0 |
| 2024 | 2024-01-01 00:00:00 UTC | 2025-01-01 00:00:00 UTC | 1 | 1 | 0 |
What Hacker News says
9 sourcesaHash claims it is faster than t1ha[1].
The t1ha crate also hasn't been updated in over three years so the benchmark in this link should be current.
[1] https://github.com/tkaitchuck/aHash/blob/master/compare/read...
Edit: if you really think tha1 is faster I would open an issue on the aHash repo to update their benchmark.
In New ScyllaDB Go Driver: Faster Than GoCQL and Its Rust CounterpartThese seem decent:
https://github.com/tkaitchuck/aHash/blob/master/FAQ.md
In New ScyllaDB Go Driver: Faster Than GoCQL and Its Rust CounterpartThe PR I have lets you provide the algorithm as the caller, although I did benchmark against fxhash and I think it would be a good idea to suggest `ahash`. I'm certainly interested.
`ahash` has some good benchmarks here:
https://github.com/tkaitchuck/aHash/blob/master/FAQ.md
In New ScyllaDB Go Driver: Faster Than GoCQL and Its Rust CounterpartThere are probably a bunch of reasons, which is why I want an easy "run benchmarks" command that I can use. I'd even be fine using infra so long as I had pulumi/terraform to set it all up for me.
I just don't want to spin up EC2 instances manually, get the connections all working, make sure I can reset state, etc.
I already have a fork of Scylla where I removed a lot of unnecessary cloning of `String` but no way I'm gonna PR it without a benchmark.
I also opened a PR to replace the hash algorithm used in their PreparedStatement cache, which gets hit for every query, but they wanted benchmarks before accepting (completely fair) and I have none. `ahash` is extremely fast compared to Rust's default - https://github.com/tkaitchuck/ahash and with the `comptime` randomness (more than sufficient for the scylla use case) you can avoid a system ca
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ll when creating the HashMap.
There are also some performance improvements I have in mind for the response parsing, among other things.
When I recently went shopping for fast hashes for short strings, I settled on wyhash, but ahash[0] seemed like it would have been better if I had bothered to port it from Rust.
> In that time you can FNV-1a a "short" string.
Not if you read it one byte at a time like in TFA!
It looks like the best FNV for short strings in smhasher[1] is comparably fast to ahash[2] on short strings.
> From the top of my head, t1ha, falkhash, meowhash and metrohash are using AES-NI and none of them are particularly fast on short inputs, and at least two of them have severe issues, despite guarding against lots of vulnerabilities, which your construction does not.
For issues like reading past the ends of buffers and discarding the extra values, it would be nice if programmers could arrange to have buffers that could be used this way. I posted a thing for has
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hing strings of a fixed length though, to compare with the thing for hashing strings of a fixed length in TFA.
Edit: It looks like your fastest FNV[3] has some issues where it repeatedly increments `p` but reads relative to `uPtr` which is not being incremented. It also seems to expect C# to have some unusual properties like (*uPtr + 4) being parsed as (*(uPtr + 4)) and being equivalent to uPtr[1] when uPtr is a pointer to a type that's 4 bytes wide (I don't know if C# actually has these properties). This may explain why your fastest FNV is much, much faster than the fastest FNV at smhasher.
FNV1a-YT also employs a good trick to avoid the issue of long data dependency chains made of multiplies: it just has three of them and only does a multiply for half of the input words in each of those. While this is fine, I'm not sure if it's really FNV-1a anymore.
[0]: https://github.com/tkaitchuck/aHash/blob/master/src/aes_hash...
[1]: https://github.com/rurban/smhasher/blob/master/doc/FNV1a_YT....
[2]: https://github.com/rurban/smhasher/blob/master/doc/ahash64.t...
[3]: https://github.com/Genbox/FastHash/blob/master/src/FastHash/...
Apparently there is a patch for the SMHasher here which adds support for ahash:
https://github.com/tkaitchuck/aHash/tree/master/smhasher
There are also ahash's own benchmarks here:
https://github.com/tkaitchuck/aHash/blob/master/compare/test...
They use the wyhash Rust crate, so if wyhash itself was updated doing a head to head comparison would boil down to updating the wyhash crate and rerunning ahash's benchmark suite.
In New Bare Hash Map: 2X-3X Speedup over SOTAAccording to this ahash is faster:
https://github.com/tkaitchuck/aHash/blob/master/compare/read...
Did anything change?
In New Bare Hash Map: 2X-3X Speedup over SOTAComparing ahash to other hashing algorithms
18 points · Open discussion