About: consistent hashing

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ӋԍӏӑӞԍӠӧӜӏӾʂҍ҅ѥ҈ ӬӆӏӮװɒױґҭѭѷҵ

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ѵѵ҉ѥѧӧӜӏԍӇҊґ

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Ό਺ҐӄـҴΌ਺ҐӦـӡҍðҬƾ҈ҁѥ  Ҋѥѧī୊

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׏ֿ ׏׀ ׏ׁ ׏ׅ ׏׆ ׏ׇ ׏ֿ־ ׏ֿ ׏׀ ׏ׁ ׏ׂ ׏׃ ׏ׄ ӄـ Ӧـӡ

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׏ֿ ׏׀ ׏ׁ ׏ׅ ׏׆ ׏ׇ ׏ֿ־ ׏ֿ ׏׀ ׏ׁ ׏ׂ ׏׃ ׏ׄ ˅૝ˤҍґѵѧҌ҆҈ҝѹѥ Ӧـӡ

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ѵҮѮ҉ѯҭҊ ؆!׌ҐӏӼـӟҺԍӇ ؆ӄӼӜӏӾҐåࢄشࠓ´҆҈ҭҥ҅ ؆Ҍҍѭѣҭҥ҅ҴҌҵѭͮѥײѺҍåð ……ҊѭҠѣѥүѥүҊ¸ê

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˕ӏԍӯԃҌȠʂ פӺӐӾԅʂץ

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׏ֿ ׏׀ ׏ׁ ׏ֿ ׏׀ ׏ׁ %3 = 1 %3 = 2 %3 = 0 ׏ׂ %3 = 1 ӺӐӾԅʂ Ӧـӡ਺Ґ৒²ҴҊҭ ׏׃ ׏ׄ %3 = 2 %3 = 0

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ӺӐӾԅʂ׋ ؆ÅҬѮχѵҫҌѱ҈ͮѷѿѧ ؆ӏԍӯԃ ؆ӦـӡҴϟՃѻҭҊѯҍŖő

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ӺӐӾԅʂ ׏ֿ ׏׀ ׏ׁ ׏ֿ ׏׀ ׏ׁ %3 = 1 %3 = 2 %3 = 0 ׏ׂ %3 = 1 ׏׃ ׏ׄ %3 = 2 %3 = 0

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ӺӐӾԅʂ ׏ׂ ׏ֿ ׏׀ ׏ׁ ׏ֿ ׏׀ ׏ׁ %3 = 1 %3 = 2 %3 = 0 ׏ׂ %3 = 1 ׏׃ ׏ׄ %3 = 2 %3 = 0

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׏ֿ ׏׀ ׏ׁ ׏ֿ ׏׀ ׏ׁ %4 = 1 %4 = 2 %4 = 3 ׏ׂ %4 = 0 ӺӐӾԅʂ ׏ׂ ׏׃ ׏ׄ %4 = 1 %4 = 2 ӦـӡҴϟՃѻҭҊѯҍŖő׎׎׎ ׏׀¦߱ѻқ҈҉ȳѯȈѩѮˠੜ

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פӺӐӾԅʂץґ ࣮ΆѮ؆୯҂ѮӦـӡҐϟՃ؏࡟আѮŖő

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ӋԍӏӑӞԍӠӧӜӏӾʂ • @_LE@YJFYF[@Q׌،TSZLZ[FS[ @ZKLSJ@SE@SETR YFFZ׋LZ[YLC\[FE@DKLSJYT[TDTQZITYFQLF_LSJ T[ WT[ZTS[KF"TYQE"LEF"FC،׮ׇׇֿׅׯ • ࣮ΆҊѹ҈ґFRD@DKFEҐҁңҐF[@R@ѮȵĚ  K[[WZ׋זזJL[K\CאDTRזזPF[@R@ • SJLSa׍W@DKFY@IILDFY_FYҤ࠾ˉ

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ӋԍӏӑӞԍӠӧӜӏӾʂ׋ ؆ӧӜӏӾВ਺ґɠҍåƖѻҭґѼ ؆ӧӜӏӾВ਺ҴԂԍӇҍѹ҈࣮Ά

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׏ֿ ׏׀ ׏ׁ ӋԍӏӑӞԍӠӧӜӏӾʂ  Ӧـӡ׍ӄـҐѿҮҀҮҴęѺӧӜӏӾ̌БҍࣹӨ @ZK׮ @ZK׮ @ZK׮ ׯ ׯ ׯ ӧӜӏӾ̌Б

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׏ֿ ׏׀ ׏ׁ @ZK׮ @ZK׮ @ZK׮ ׯ ׯ ׯ ӧӜӏӾ̌Б ׏ֿ ׏׀ ׏ׁ ׏ׂ ׏׃ ׏ׄ @ZK׮ @ZK׮ @ZK׮ @ZK׮ @ZK׮ @ZK׮ ׯ ׯ ׯ ׯ ׯ ׯ ӋԍӏӑӞԍӠӧӜӏӾʂ  Ӧـӡ׍ӄـҐѿҮҀҮҴęѺӧӜӏӾ̌БҍࣹӨ

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׏ֿ @ZK׮ ׯ ׏ֿ ׏׀ ׏ׁ @ZK׮ @ZK׮ @ZK׮ ׯ ׯ ׯ ۙѥÃҴબ୒ ׏ֿ ׏׀ ׏ׁ ׏ׂ ׏׃ ׏ׄ @ZK׮ @ZK׮ @ZK׮ @ZK׮ @ZK׮ @ZK׮ ׯ ׯ ׯ ׯ ׯ ׯ ֿ˕ҐÃҴҊҭ ؼ ӧӜӏӾ̌Б ӋԍӏӑӞԍӠӧӜӏӾʂ  Ӧـӡ׍ӄـҐѿҮҀҮҴęѺӧӜӏӾ̌БҍࣹӨ

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ӋԍӏӑӞԍӠӧӜӏӾʂ׋ ؆ӧӜӏӾВ਺ґɠҍåƖѻҭґѼ  ؕҌҐ҉ÅҫҌѥ ؆ȳѯȈҰҭҐґӧӜӏӾ̌БҐ϶҂ѳҐґѼ  ؕҌҐ҉ϟՃѹҁҊѯҐӘӹـӐѮƀҌѥ

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׏ֿ ׏׀ ׏ׁ ϟՃѹҁҊѯҐӘӹـӐѮƀҌѥ @ZK׮ @ZK׮ @ZK׮ ׯ ׯ ׯ ӧӜӏӾ̌Б ׏ֿ ׏׀ ׏ׁ ׏ׂ ׏׃ ׏ׄ @ZK׮ @ZK׮ @ZK׮ @ZK׮ @ZK׮ @ZK׮ ׯ ׯ ׯ ׯ ׯ ׯ

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ϟՃѹҁҊѯҐӘӹـӐѮƀҌѥ ӧӜӏӾ̌Б ׏ֿ ׏׀ ׏ׁ ׏ׂ ׏׃ ׏ׄ @ZK׮ @ZK׮ @ZK׮ @ZK׮ @ZK׮ @ZK׮ ׯ ׯ ׯ ׯ ׯ ׯ ׏ֿ ׏׀ ׏ׁ @ZK׮ @ZK׮ @ZK׮ ׯ ׯ ׯ ׏ׂ @ZK׮ ׯ ׏ׂҴϟՃ

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ϟՃѹҁҊѯҐӘӹـӐѮƀҌѥ ӧӜӏӾ̌Б ׏ֿ ׏׀ ׏ׁ ׏ׂ ׏׃ ׏ׄ @ZK׮ @ZK׮ @ZK׮ @ZK׮ @ZK׮ @ZK׮ ׯ ׯ ׯ ׯ ׯ ׯ ׏ֿ ׏׀ ׏ׁ @ZK׮ @ZK׮ @ZK׮ ׯ ׯ ׯ ۙѥÃҴબ୒ ׏ׂ @ZK׮ ׯ ȳѯȈҰ҆ҁҐґ׏ׄ҂ѳ׎

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ӋԍӏӑӞԍӠӧӜӏӾʂ׋ ؆ÅҫҌѥ ؆ϟՃѹҁҊѯҐӘӹـӐѮƀҌѥ

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ӧӜӏӾ̌Б ׏ֿ @ZK׮ ׯ ˅૝ˤҍґ ؟ֿذ׀׋

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˅૝ˤҍґ ӧӜӏӾ̌Б ׏ֿ ׏׀ @ZK׮ @ZK׮ ׯ ׯ ׏׀ҴϟՃѻҭҊ ؟ֿذ׀׋׃־أ

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ӧӜӏӾ̌Б ׏ֿ ׏׀ @ZK׮ @ZK׮ ׯ ׯ ׏ׁ @ZK׮ ׯ ˅૝ˤҍґ ؟׀ذׁ׋׀׃أ ׏ׁҴϟՃѻҭҊ

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ӧӜӏӾ̌Б ׏ֿ ׏׀ @ZK׮ @ZK׮ ׯ ׯ ׏ׁ @ZK׮ ׯ ׏ׂ @ZK׮ ׯ ˅૝ˤҍґ ؟ׁذׂ׋׀׃أ ׏ׂҴϟՃѻҭҊ

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ӋԍӏӑӞԍӠӧӜӏӾʂ׋ ؆ÅҫҌѥ ؆ϟՃѹҁҊѯҐӘӹـӐѮƀҌѥ

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ӋԍӏӑӞԍӠӧӜӏӾʂҐ࣮Ά  ׮F[@R@ҐńĘׯ

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# ϋογϡؔ਺͸32bit unsigned intͷϋογϡ஋Λฦ͢  # CRC32, MD5ͷ্Ґ32bitͳͲͰ࣮૷  func hash(key string) uint32 { ... } # ϊʔυͷϋογϡ஋Λܭࢉ for _, node := range nodes { # ͻͱͭͷϊʔυຖʹ160ݸͷϋογϡΛܭࢉ for i := 0; i < 160; i++ { k := fmt.Sprintf(“%s-%d”, node, i)    # ϊʔυ໊ͱϋογϡ஋ͷϖΞΛ௥Ճ continuum.add(node, hash(k)) } } # ϋογϡ஋Ͱιʔτ͓ͯ͘͠ sort.Sort(continuum) ֿאӦـӡӶӜӯҐܭࢉ

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ֿאӦـӡӶӜӯҐܭࢉ ӧӜӏӾ̌Б ׏ֿ @ZK׮ ׯ ֿ҅ҐӦـӡҍରѹ  Ό਺ҐӧӜӏӾҴܭࢉ  ذӧӜӏӾܭࢉҍҩҭÅҬҴЕɦ ؕ׮׀־־¿ѱҫѥ҉ůŲׯ

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# ϋογϡ஋Ͱιʔτ͓͚ͯ͠͹ೋ෼୳ࡧͰ୳ࡧͰ͖Δ  func search(key string) string { v := hash(key) i, j := 0, n for i < j { h := i + (j-i)/2 if (continuum.values[i] > v) { i = h + 1 } else { j = h } } return continuum.nodes[i] } ׀אӧӜӏӾҐ୳ࡧ

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׀אӧӜӏӾҐ୳ࡧ ӧӜӏӾ̌Б _ @ZK׮ ׯ ׏ֿ ׏׀ ׏ׁ @ZK׮ @ZK׮ @ZK׮ ׯ ׯ ׯ ׏ׂ @ZK׮ ׯ å୳ࡧ҉˕ۙѥӧӜӏӾҴʹŲ

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ҠҊң  ׮ӋԍӏӑӞԍӠӧӜӏӾʂׯ ؆ÅҫҌѥ  ؕӧӜӏӾВ਺Ҋѹ҈ґ׃¯ׁ׀CL[׌ׁ׀׌!؆ֿ̙ ؆ϟՃѹҁҊѯҐӘӹـӐѮƀҌѥ  ؆࣮ΆҤӏԍӯԃ