Home > NoSQL, Oracle, SQL > What’s so sacred about relational anyway?

What’s so sacred about relational anyway?


Eventual Consistency!

Dr. Codd was acutely aware of the potential overhead of consistency checking. In the concluding section of his famous paper, he says: “There are, of course, several possible ways in which a system can detect inconsistencies and respond to them. In one approach the system checks for possible inconsistency whenever an insertion, deletion, or key update occurs. Naturally, such checking will slow these operations down. [emphasis added] If an inconsistency has been generated, details are logged internally, and if it is not remedied within some reasonable time interval, either the user or someone responsible for the security and integrity of the data is notified. Another approach is to conduct consistency checking as a batch operation once a day or less frequently. Inputs causing the inconsistencies which remain in the data bank state at checking time can be tracked down if the system maintains a journal of all state-changing transactions. This latter approach would certainly be superior if few non-transitory inconsistencies occurred.”

This approach can be dubbed “eventual consistency” and is used by NoSQL systems; for example, distributed replicas may go out of sync in a NoSQL cluster. It is ironic that a principle elucidated by Dr. Codd in the first paper on relational theory should have found its first application in systems that reject relational theory.

Answers to quiz questions: 1 (a), 2 (a), 3 (a)

Pages: 1 2 3 4

Categories: NoSQL, Oracle, SQL
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