Skip to content

Instantly share code, notes, and snippets.

Embed
What would you like to do?

A Bloom Filter in Redis

This is a really simple implementation of a bloom filter using Redis 2.6's lua scripting facility.

Though it "works", it's just a proof of concept. The choice and implementation of hashing functions leave something to be desired (I'm sure it's a fine implementation of CRC32 that I borrowed, but it's in pure lua, and, well, CRC32 is not the best function to use for a bloom filter).

Caveat Emptor, no refunds, etc. MIT License.

--
-- bloom_filter_get.lua
--
-- Usage:
-- EVAL (script) filtername key iterations filtersize
--
-- Arguments:
-- filtername: The key the bloom filter is stored in
-- key: The key to search the filter for
-- iterations: Number of hashes to calculate for each value
-- filtersize: Number of buckets (bits) to use for the filter
--
local filter = KEYS[1]
local key = KEYS[2]
local iterations = tonumber(KEYS[3])
local filtersize = tonumber(KEYS[4])
-- CRC32 lib follows, program resumes on line 90.
-- Copyright (c) 2007-2008 Neil Richardson (nrich@iinet.net.au) under MIT License
local max = 2^32 -1
local CRC32 = { 0,79764919,159529838,222504665,319059676, 398814059,445009330,507990021,638119352, 583659535,797628118,726387553,890018660, 835552979,1015980042,944750013,1276238704, 1221641927,1167319070,1095957929,1595256236, 1540665371,1452775106,1381403509,1780037320, 1859660671,1671105958,1733955601,2031960084, 2111593891,1889500026,1952343757,2552477408, 2632100695,2443283854,2506133561,2334638140, 2414271883,2191915858,2254759653,3190512472, 3135915759,3081330742,3009969537,2905550212, 2850959411,2762807018,2691435357,3560074640, 3505614887,3719321342,3648080713,3342211916, 3287746299,3467911202,3396681109,4063920168, 4143685023,4223187782,4286162673,3779000052, 3858754371,3904687514,3967668269,881225847, 809987520,1023691545,969234094,662832811, 591600412,771767749,717299826,311336399, 374308984,453813921,533576470,25881363, 88864420,134795389,214552010,2023205639, 2086057648,1897238633,1976864222,1804852699, 1867694188,1645340341,1724971778,1587496639, 1516133128,1461550545,1406951526,1302016099, 1230646740,1142491917,1087903418,2896545431, 2825181984,2770861561,2716262478,3215044683, 3143675388,3055782693,3001194130,2326604591, 2389456536,2200899649,2280525302,2578013683, 2640855108,2418763421,2498394922,3769900519, 3832873040,3912640137,3992402750,4088425275, 4151408268,4197601365,4277358050,3334271071, 3263032808,3476998961,3422541446,3585640067, 3514407732,3694837229,3640369242,1762451694, 1842216281,1619975040,1682949687,2047383090, 2127137669,1938468188,2001449195,1325665622, 1271206113,1183200824,1111960463,1543535498, 1489069629,1434599652,1363369299,622672798, 568075817,748617968,677256519,907627842, 853037301,1067152940,995781531,51762726, 131386257,177728840,240578815,269590778, 349224269,429104020,491947555,4046411278, 4126034873,4172115296,4234965207,3794477266, 3874110821,3953728444,4016571915,3609705398, 3555108353,3735388376,3664026991,3290680682, 3236090077,3449943556,3378572211,3174993278, 3120533705,3032266256,2961025959,2923101090, 2868635157,2813903052,2742672763,2604032198, 2683796849,2461293480,2524268063,2284983834, 2364738477,2175806836,2238787779,1569362073, 1498123566,1409854455,1355396672,1317987909, 1246755826,1192025387,1137557660,2072149281, 2135122070,1912620623,1992383480,1753615357, 1816598090,1627664531,1707420964,295390185, 358241886,404320391,483945776,43990325, 106832002,186451547,266083308,932423249, 861060070,1041341759,986742920,613929101, 542559546,756411363,701822548,3316196985, 3244833742,3425377559,3370778784,3601682597, 3530312978,3744426955,3689838204,3819031489, 3881883254,3928223919,4007849240,4037393693, 4100235434,4180117107,4259748804,2310601993, 2373574846,2151335527,2231098320,2596047829, 2659030626,2470359227,2550115596,2947551409, 2876312838,2788305887,2733848168,3165939309, 3094707162,3040238851,2985771188, }
local function xor(a, b)
local calc = 0
for i = 32, 0, -1 do
local val = 2 ^ i
local aa = false
local bb = false
if a == 0 then
calc = calc + b
break
end
if b == 0 then
calc = calc + a
break
end
if a >= val then
aa = true
a = a - val
end
if b >= val then
bb = true
b = b - val
end
if not (aa and bb) and (aa or bb) then
calc = calc + val
end
end
return calc
end
local function lshift(num, left)
local res = num * (2 ^ left)
return res % (2 ^ 32)
end
local function rshift(num, right)
local res = num / (2 ^ right)
return math.floor(res)
end
function Hash(str)
local count = string.len(tostring(str))
local crc = max
local i = 1
while count > 0 do
local byte = string.byte(str, i)
crc = xor(lshift(crc, 8), CRC32[xor(rshift(crc, 24), byte) + 1])
i = i + 1
count = count - 1
end
return crc
end
-- END CRC32
local curr = key
for i=1, iterations, 1 do
curr = Hash(curr)
val = redis.call('GETBIT', filter, curr % filtersize)
if val == 0 then return false end
end
return true
--
-- bloom_filter_set.lua
--
-- Usage:
-- EVAL (script) filtername key iterations filtersize
--
-- Arguments:
-- filtername: The key to store the bloom filter in
-- key: The key to insert into the filter
-- iterations: Number of hashes to calculate for each value
-- filtersize: Number of buckets (bits) to use for the filter
--
local filter = KEYS[1]
local key = KEYS[2]
local iterations = tonumber(KEYS[3])
local filtersize = tonumber(KEYS[4])
-- CRC32 lib follows, program resumes on line 90.
-- Copyright (c) 2007-2008 Neil Richardson (nrich@iinet.net.au) under MIT License
local max = 2^32 -1
local CRC32 = { 0,79764919,159529838,222504665,319059676, 398814059,445009330,507990021,638119352, 583659535,797628118,726387553,890018660, 835552979,1015980042,944750013,1276238704, 1221641927,1167319070,1095957929,1595256236, 1540665371,1452775106,1381403509,1780037320, 1859660671,1671105958,1733955601,2031960084, 2111593891,1889500026,1952343757,2552477408, 2632100695,2443283854,2506133561,2334638140, 2414271883,2191915858,2254759653,3190512472, 3135915759,3081330742,3009969537,2905550212, 2850959411,2762807018,2691435357,3560074640, 3505614887,3719321342,3648080713,3342211916, 3287746299,3467911202,3396681109,4063920168, 4143685023,4223187782,4286162673,3779000052, 3858754371,3904687514,3967668269,881225847, 809987520,1023691545,969234094,662832811, 591600412,771767749,717299826,311336399, 374308984,453813921,533576470,25881363, 88864420,134795389,214552010,2023205639, 2086057648,1897238633,1976864222,1804852699, 1867694188,1645340341,1724971778,1587496639, 1516133128,1461550545,1406951526,1302016099, 1230646740,1142491917,1087903418,2896545431, 2825181984,2770861561,2716262478,3215044683, 3143675388,3055782693,3001194130,2326604591, 2389456536,2200899649,2280525302,2578013683, 2640855108,2418763421,2498394922,3769900519, 3832873040,3912640137,3992402750,4088425275, 4151408268,4197601365,4277358050,3334271071, 3263032808,3476998961,3422541446,3585640067, 3514407732,3694837229,3640369242,1762451694, 1842216281,1619975040,1682949687,2047383090, 2127137669,1938468188,2001449195,1325665622, 1271206113,1183200824,1111960463,1543535498, 1489069629,1434599652,1363369299,622672798, 568075817,748617968,677256519,907627842, 853037301,1067152940,995781531,51762726, 131386257,177728840,240578815,269590778, 349224269,429104020,491947555,4046411278, 4126034873,4172115296,4234965207,3794477266, 3874110821,3953728444,4016571915,3609705398, 3555108353,3735388376,3664026991,3290680682, 3236090077,3449943556,3378572211,3174993278, 3120533705,3032266256,2961025959,2923101090, 2868635157,2813903052,2742672763,2604032198, 2683796849,2461293480,2524268063,2284983834, 2364738477,2175806836,2238787779,1569362073, 1498123566,1409854455,1355396672,1317987909, 1246755826,1192025387,1137557660,2072149281, 2135122070,1912620623,1992383480,1753615357, 1816598090,1627664531,1707420964,295390185, 358241886,404320391,483945776,43990325, 106832002,186451547,266083308,932423249, 861060070,1041341759,986742920,613929101, 542559546,756411363,701822548,3316196985, 3244833742,3425377559,3370778784,3601682597, 3530312978,3744426955,3689838204,3819031489, 3881883254,3928223919,4007849240,4037393693, 4100235434,4180117107,4259748804,2310601993, 2373574846,2151335527,2231098320,2596047829, 2659030626,2470359227,2550115596,2947551409, 2876312838,2788305887,2733848168,3165939309, 3094707162,3040238851,2985771188, }
local function xor(a, b)
local calc = 0
for i = 32, 0, -1 do
local val = 2 ^ i
local aa = false
local bb = false
if a == 0 then
calc = calc + b
break
end
if b == 0 then
calc = calc + a
break
end
if a >= val then
aa = true
a = a - val
end
if b >= val then
bb = true
b = b - val
end
if not (aa and bb) and (aa or bb) then
calc = calc + val
end
end
return calc
end
local function lshift(num, left)
local res = num * (2 ^ left)
return res % (2 ^ 32)
end
local function rshift(num, right)
local res = num / (2 ^ right)
return math.floor(res)
end
function Hash(str)
local count = string.len(tostring(str))
local crc = max
local i = 1
while count > 0 do
local byte = string.byte(str, i)
crc = xor(lshift(crc, 8), CRC32[xor(rshift(crc, 24), byte) + 1])
i = i + 1
count = count - 1
end
return crc
end
-- END CRC32
local curr = key
for i=1, iterations, 1 do
curr = Hash(curr)
redis.call('SETBIT', filter, curr % filtersize, 1)
end
return "OK"
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
You can’t perform that action at this time.