Data Property - ACID (atomicity, consistency, isolation, durability)

1 - About

In computer science, ACID (atomicity, consistency, isolation, durability) is a set of properties that guarantee transactions are processed reliably.

They defines a concurrency model.

Traditional database (ie non distributed database) follows this rules. In a distributed database, traditional database would be categorize as the AC type of the cap theorem. Conventional databases assume no network partitioning and are not distributed.

3 - ACID rules

Ideally, the software should enforce the ACID rules, summarized here:

  • Atomicity: Either all the tasks in a transaction must happen, or none of them. The transaction must be completed, or else it must be undone (rolled back). Atomicity = the Transaction must fail of succeed. Either all occur or none of them occur.
  • Consistency: Every transaction must preserve the integrity constraints — the declared consistency rules — of the database. It cannot leave the data in a contradictory state. A series of database operations does not violate any integrity constraints during execution.
  • Isolation: Two simultaneous transactions cannot interfere with one another. Intermediate results within a transaction must remain invisible to other transactions. The intermediate state of a series of database operations cannot be seen by other series of database operations.
  • Durability: Completed transactions cannot be aborted later or their results discarded. They must persist through (for instance) restarts of the DBMS after crashes. A series of database operations that have committed are guaranteed to survive permanently.

4 - Weaker concurrency model

In practice, many DBMSs allow the selective relaxation of most of these rules — for better performance or on a distributed system

5 - Documentation / Reference

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