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51 lines
1.1 KiB
Go
51 lines
1.1 KiB
Go
package netstorage
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import (
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"github.com/cespare/xxhash/v2"
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)
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// See the following docs:
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// - https://www.eecs.umich.edu/techreports/cse/96/CSE-TR-316-96.pdf
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// - https://github.com/dgryski/go-rendezvous
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// - https://dgryski.medium.com/consistent-hashing-algorithmic-tradeoffs-ef6b8e2fcae8
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type consistentHash struct {
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hashSeed uint64
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nodeHashes []uint64
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}
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func newConsistentHash(nodes []string, hashSeed uint64) *consistentHash {
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nodeHashes := make([]uint64, len(nodes))
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for i, node := range nodes {
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nodeHashes[i] = xxhash.Sum64([]byte(node))
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}
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return &consistentHash{
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hashSeed: hashSeed,
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nodeHashes: nodeHashes,
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}
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}
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func (rh *consistentHash) getNodeIdx(h uint64, excludeIdxs []int) int {
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var mMax uint64
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var idx int
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h ^= rh.hashSeed
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next:
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for i, nh := range rh.nodeHashes {
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for _, j := range excludeIdxs {
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if i == j {
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continue next
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}
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}
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if m := fastHashUint64(nh ^ h); m > mMax {
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mMax = m
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idx = i
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}
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}
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return idx
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}
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func fastHashUint64(x uint64) uint64 {
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x ^= x >> 12 // a
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x ^= x << 25 // b
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x ^= x >> 27 // c
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return x * 2685821657736338717
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}
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