First step of “Chord”

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First step of “Chord” 2016-09-23 ࣾ಺ษڧձ @kakakakakku

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Cloud Computing Concepts, Part 1 by

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࠷ۙ Coursera Ͱ ཤमͯ͠ΔߨٛͰֶΜͩ “Chord” ΛβοΫϦͱ঺հ͠·͢

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What is “Chord” ?

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(ƅшƅ) ŴƅŜŖƃ ?

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εέʔϥϏϦςΟͷ͋Δ P2P ୳ࡧΞϧΰϦζϜʢҙ༁ʣ → ൃද͸2001೥

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[Related Algorithms] Tapestry Pastry Kademlia ʘ ࠓ೔͸঺հ͠ͳ͍͚Ͳଞʹ΋͋Δ ʗ

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[Related Implementation] Cassandra Dynamo Riak Voldemort ʘ ϛυϧ΢ΣΞΛΠϝʔδ͢Δͱ਌ۙײ༙͘ ʗ

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ʘ Dynamo ͷ࿦จ΋·ͨผͷػձʹ঺հ͠·͢ ʗ

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P2P Λ෼ྨ͢Δͱ...

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Unstructured Overlay Structured Overlay Chord Napster / Gnutella

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Goal of “Chord”

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େྔͷΩʔΛͲ͏෼ࢄͤ͞Δ ? େྔͷΩʔΛͲ͏ޮ཰తʹ୳ࡧͤ͞Δ ? ϊʔυͷ૿ݮʹͲ͏ରԠ͢Δ ?

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“Chord” = Consistent Hashing + Finger Table

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(ƅшƅ) Űō?

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Consistent Hashing ղઆ

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ҰݴͰද͢ͱ Ωʔͷ࠶഑ஔͷӨڹΛ࡟ݮͨ͠ ޮ཰తͳϋογϡ๏ʢҙ༁ʣ

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Bad Example ʘ ࠷ॳʹμϝͳྫΛݟͯΈ·͠ΐ͏ ʗ

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3 Nodes 4 Keys ΩϨΠʹ ෼ࢄͨ͠ ??? ୯७ʹ mod ͰΩʔΛϊʔυʹ഑ஔ͢Δͱ...

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΋͠1୆ ނোͨ͠৔߹ ΦϨϯδҎ֎ શͯͷΩʔΛ࠶഑ஔ ͢Δඞཁ͕͋Δ

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Consistent Hashing ొ৔

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ϊʔυͱΩʔΛϋογϡԽͯ͠ Ծ૝Ϧϯά্ʹ഑ஔ͢Δ ※Ծ૝ͷҙຯ͸ࠓճ͸ׂѪ͠·͢...

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֤Ωʔ͔Βݟͯ ࣌ܭճΓʹ1൪ۙ઀ͨ͠ϊʔυʹ ΩʔΛ഑ஔ͢Δͱ͍͏ߟ͑ํ ʢͦͷϊʔυ͸ Successor ͱݺͿʣ

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Ϧϯάۭؒ ഑ஔ ഑ஔ ഑ஔ

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Ϧϯάۭؒ ނোͰ࠶഑ஔ͕ඞཁͳΩʔ਺͸ ʹ࡟ݮ͞ΕΔ ഑ஔ ࠶഑ஔ ഑ஔ

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Αͬͯ ϊʔυ௥Ճʗނোʢҙਤతͳݮগ΋ʣ ʹରͯ͠ ہॴతͳӨڹʹ཈͑ΒΕΔ

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Finger Table ղઆ

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Chord ͷಛ௃తͳ࢓૊Έ ! ҰݴͰද͢ͱγϣʔτΧοτతͳ ?

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Bad Example ʘ ࠷ॳʹμϝͳྫΛݟͯΈ·͠ΐ͏ ʗ

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୳ࡧ͢Δͱ͖ʹ key ͕͋Δ ୳ࡧΛϦΫΤετ ͢Δϊʔυ

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ϊʔυΛॱ൪ʹḷͬͯ͠·͏ͱ ઢܗ୳ࡧʹͳͬͯ͠·͏… ʘ Oh, No! ʗ

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Finger Table ొ৔

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೚ҙͷϊʔυʹରͯ͠ ࢦ਺ؔ਺తʹ୳ࡧՄೳͳ ϩέʔγϣϯʢҙ༁ʣΛఆΊͯ ଟஈ֊ʹ୳ࡧͤ͞Δ

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͜ͷྫͩͱ m=3 ͰޮՌ͕ແͦ͞͏ʹݟ͑Δ͚Ͳ... Finger Table

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ઢܗ୳ࡧΛճආͰ͖ΔͨΊ ۭؒͷεέʔϦϯάʹରͯ͠ ୳ࡧ࣌ؒ͸େ͖͘ࠨӈ͞Εͳ͘ͳΔ ʘ Good! ʗ

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“Chord” = Consistent Hashing + Finger Table ʘ βοΫϦͱཧղͯ͠΋Β͑ͨ ? ʗ

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࣮ࡍͷ “Chord” Ͱ͸ ϊʔυΛ SHA-1(ip, port) Ͱ഑ஔͯ͠ ΩʔΛ SHA-1(key) Ͱ഑ஔ͢Δ ※SHA-1 ͳΒ 160 bit ͷۭؒͰදݱͰ͖Δ

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·ͱΊ

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೔ʑ࢖ͬͯΔٕज़͸ ੈքதͷεΰΠਓ͕ͨͪߟ͑ͨ ΞϧΰϦζϜʹࢧ͑ΒΕ͍ͯΔʂ