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by doverton 4376 days ago
"Consistency around CAP is similar to what you find in a typical ACID model - except that, now, we're in a distributed model."

I thought that consistency in ACID meant that data was always consistent with the rules of the database, whereas in CAP it means that the same data held in different locations is the same? Is that not right?
2 comments
Dave_Rosenthal 4376 days ago
You are right. The article is totally wrong.

From Eric Brewer himself: "The relationship between CAP and ACID is more complex and often misunderstood, in part because the C and A in ACID represent different concepts than the same letters in CAP..."

(from http://www.infoq.com/articles/cap-twelve-years-later-how-the...)

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fh973 4376 days ago
No, the data in different locations does not need to be the same (think: quorum operations).

Consistent means that they are consistent from the perspective of the client within the rules of the consistency model. If you have sequential consistency and quorum operations, your replicas do not need to have the same data, but the view of your clients is always consistent.

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