├── README.md
└── chash.lua


/README.md:
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 1 | lua-consistent-hash
 2 | ===================
 3 | 
 4 | A reimplementation of consistent hash in lua based on yaoweibin's fork of consistent hash (https://github.com/yaoweibin/ngx_http_consistent_hash)
 5 | 
 6 | Usage
 7 | -----
 8 | 
 9 | ```lua
10 | local chash = require "chash"
11 | 
12 | chash.add_upstream("192.168.0.251")
13 | chash.add_upstream("192.168.0.252")
14 | chash.add_upstream("192.168.0.253")
15 | 
16 | local upstream = chash.get_upstream("my_hash_key")
17 | ```


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/chash.lua:
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  1 | local M = {}
  2 | M.initialized = false
  3 | 
  4 | local MMC_CONSISTENT_BUCKETS = 65536
  5 | 
  6 | local HASH_PEERS = {}
  7 | local CONTINUUM = {}
  8 | local BUCKETS = {}
  9 | 
 10 | local function hash_fn(key)
 11 | 	local md5 = ngx.md5_bin(key) --nginx only
 12 | 	return ngx.crc32_long(md5) --nginx only
 13 | end
 14 | 
 15 | --in-place quicksort
 16 | local function quicksort(t, start, endi)
 17 | 	start, endi = start or 1, endi or #t
 18 | 	--partition w.r.t. first element
 19 | 	if(endi - start < 2) then return t end
 20 | 	local pivot = start
 21 | 	for i = start + 1, endi do
 22 | 		if t[i][2] < t[pivot][2] then
 23 | 			local temp = t[pivot + 1]
 24 | 			t[pivot + 1] = t[pivot]
 25 | 			if(i == pivot + 1) then
 26 | 				t[pivot] = temp
 27 | 			else
 28 | 				t[pivot] = t[i]
 29 | 				t[i] = temp
 30 | 			end
 31 | 			pivot = pivot + 1
 32 | 		end
 33 | 	end
 34 | 	t = quicksort(t, start, pivot - 1)
 35 | 	return quicksort(t, pivot + 1, endi)
 36 | end
 37 | 
 38 | local function chash_find(point)
 39 | 	local mid, lo, hi = 1, 1, #CONTINUUM
 40 | 	while 1 do
 41 | 		if point <= CONTINUUM[lo][2] or point > CONTINUUM[hi][2] then
 42 | 			return CONTINUUM[lo]
 43 | 		end
 44 | 
 45 | 		mid = math.floor(lo + (hi-lo)/2)
 46 | 		if point <= CONTINUUM[mid][2] and point > (mid and CONTINUUM[mid-1][2] or 0) then
 47 | 			return CONTINUUM[mid]
 48 | 		end
 49 | 
 50 | 		if CONTINUUM[mid][2] < point then
 51 | 			lo = mid + 1
 52 | 		else
 53 | 			hi = mid - 1
 54 | 		end
 55 | 	end
 56 | end
 57 | 
 58 | local function chash_init()
 59 | 
 60 | 	local n = #HASH_PEERS
 61 | 
 62 | 	local ppn = math.floor(MMC_CONSISTENT_BUCKETS / n)
 63 | 	if ppn == 0 then
 64 | 		ppn = 1
 65 | 	end
 66 | 
 67 | 	local C = {}
 68 | 	for i,peer in ipairs(HASH_PEERS) do
 69 | 		for k=1, math.floor(ppn * peer[1]) do
 70 | 			local hash_data = peer[2] .. "-"..tostring(math.floor(k - 1))
 71 | 			table.insert(C, {peer[2], hash_fn(hash_data)})
 72 | 		end
 73 | 	end
 74 | 
 75 | 	CONTINUUM = quicksort(C, 1, #C)
 76 | 
 77 | 	local step = math.floor(0xFFFFFFFF / MMC_CONSISTENT_BUCKETS)
 78 | 
 79 | 	BUCKETS = {}
 80 | 	for i=1, MMC_CONSISTENT_BUCKETS do
 81 | 		table.insert(BUCKETS, i, chash_find(math.floor(step * (i - 1))))
 82 | 	end
 83 | 
 84 | 	M.initialized = true
 85 | end
 86 | 
 87 | local function chash_get_upstream(key)
 88 | 	if not M.initialized then
 89 | 		chash_init()
 90 | 	end
 91 | 
 92 | 	local point = math.floor(ngx.crc32_long(key)) --nginx only
 93 | 
 94 | 	local tries = #HASH_PEERS
 95 | 	point = point + (89 * tries)
 96 | 	local bucket_idx = point % MMC_CONSISTENT_BUCKETS
 97 |   	if bucket_idx == 0 then
 98 |     		bucket_idx = 1
 99 |   	end
100 | 	return BUCKETS[bucket_idx][1]
101 | end
102 | M.get_upstream = chash_get_upstream
103 | 
104 | local function chash_add_upstream(upstream, weight)
105 | 	M.initialized = false
106 | 
107 | 	weight = weight or 1
108 | 	table.insert(HASH_PEERS, {weight, upstream})
109 | end
110 | M.add_upstream = chash_add_upstream
111 | 
112 | return M
113 | 


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