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Question: How is hashbrown faster than the stdlib HashMap? (sh.itjust.works)

submitted 1 year ago by BolshoyToster@sh.itjust.works to c/rust@lemmy.ml

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I'm curious as to how the hashbrown crate can have up to 2x performance on certain operations, even though it looks like the standard library's HashMap is just a wrapper for hashbrown.

I understand that a wrapper could add a small overhead, but 50% of the original performance is a bit silly, especially considering all of the functions in the wrapper are #[inline], so there should be no overhead in calling most functions.

Does anyone know the reason for this?

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[–] CPU@lemdro.id 11 points 1 year ago

hashbrown uses aHash by default, which is much faster than std's SipHash-1-3

[–] anhkagi@jlai.lu 7 points 1 year ago

I suppose it's because the article you're citing is from april 22nd, and that hashbrown has replaced old std hashmap in this commit, which hash been created on 24th.

I suppose (can't test myself) that if you do the test now (hashbrown against std), the performance difference would be negligeable beacuse you would be testing roughly the same algorithms.

[–] crispy_kilt@feddit.de 2 points 1 year ago

Stdlib uses SipHash, not HashBrown.