Database
NoSQL (Not only SQL)
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Key-value
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Document
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Graph
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...
ACID
Transaction, 一連串必須要一起進行的操作，如果一個操錯失敗，所以已經執行的操作都必須取消
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Atomicity
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Consistency
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Isolation
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Durability
Just a 原子操作
CAP theorem
CAP定理101—分散式系統，有一好沒兩好. Cap Theorem 101 | by YH Yu | 後端新手村 | Medium
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Consistency: all client see all same data at same time
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Availability
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Partition tolerance: network connection
Eventually Consistency 最終一致性
保證最終會同步
Strong Consistency 強一致性
N replica
W is number of write / udpate replica
R is number of read from replica
if W + R > N, Strong Consistency
it means atleast one of the W and R are overlap