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Database - ACID
About
In computer science, ACID (atomicity, consistency, isolation, durability) is a set of properties that guarantee database transactions are processed reliably. The concept of ACID is to evaluate databases and application architecture.
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ACID rules
Ideally, the database 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).
- Consistency: Every transaction must preserve the integrity constraints — the declared consistency rules — of the database. It cannot leave the data in a contradictory state.
- Isolation: Two simultaneous transactions cannot interfere with one another. Intermediate results within a transaction must remain invisible to other transactions.
- Durability: Completed transactions cannot be aborted later or their results discarded. They must persist through (for instance) restarts of the DBMS after crashes.
In practice, many DBMSs allow the selective relaxation of most of these rules — for better performance.
