ClickHouse/base/consistent-hashing/consistent_hashing.h
2020-02-14 17:48:30 +03:00

20 lines
833 B
C++

#pragma once
#include <cstdint>
#include <cstddef>
/*
* Author: Konstantin Oblakov
*
* Maps random ui64 x (in fact hash of some string) to n baskets/shards.
* Output value is id of a basket. 0 <= ConsistentHashing(x, n) < n.
* Probability of all baskets must be equal. Also, it should be consistent
* in terms, that with different n_1 < n_2 probability of
* ConsistentHashing(x, n_1) != ConsistentHashing(x, n_2) must be equal to
* (n_2 - n_1) / n_2 - the least possible with previous conditions.
* It requires O(1) memory and cpu to calculate. So, it is faster than classic
* consistent hashing algos with points on circle.
*/
std::size_t ConsistentHashing(std::uint64_t x, std::size_t n); // Works for n <= 32768
std::size_t ConsistentHashing(std::uint64_t lo, std::uint64_t hi, std::size_t n); // Works for n <= 2^31