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Probably don't want to go back and rewrite all their past data.

Pretty much this. From the post:

"Because it produces different results, it would render all our stored checksums invalid, so we'd have to recalculate them all. That's a big job, so we'd need to do a lot of testing first to make sure that it's so much better that it's actually worth the effort."

xxHash is at least an order of magnitude faster so it might be worth upgrading.

My quick tests here (using the same methods outlined in the post) suggests its around 30% faster on 64-byte buffers. If we're ever shopping for a new hash function entirely, I'll make sure its considered. Right now its not worth it because as noted in the post, we're not actually under any particular stress and changing hash functions is a big job.

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