Short term Redis plans (opens in new tab)

(antirez.com)

14 pointsstevefink14y ago3 comments

3 comments

pork14y ago

Just curious about the key distribution algorithm -- why use CRC-16(key) % 4096 instead of a fast hash function like djb2, which almost certainly has better key equidistribution?

http://www.cse.yorku.ca/~oz/hash.html

antirez14y ago

Actually CRC-16 has a much better distribution than djb2 and other algorithms for this use case. CRC-16 is a remarkably good algorithm for certain kind of hashing, and has a few very interesting qualities being the reminder of a polynominal division. For instance if you hash two bytes data you are guaranteed to have different hashes for every different pair of bytes without collisions.

CRC-16 performed very well in tests also with the very common case of keys with the same prefix, like object:0, object:1, and so forth.

So CRC-16 is very good for our use case and has the advantage of being simple and fast.

pork14y ago

Thank you! Perhaps this warrants a blog post by itself?

j / k navigate · click thread line to collapse

3 comments

pork14y ago

Just curious about the key distribution algorithm -- why use CRC-16(key) % 4096 instead of a fast hash function like djb2, which almost certainly has better key equidistribution?

http://www.cse.yorku.ca/~oz/hash.html

antirez14y ago

CRC-16 performed very well in tests also with the very common case of keys with the same prefix, like object:0, object:1, and so forth.

So CRC-16 is very good for our use case and has the advantage of being simple and fast.

pork14y ago

Thank you! Perhaps this warrants a blog post by itself?

j / k navigate · click thread line to collapse