Niveaux d'Isolation des Transactions
Ils régulent la façon dont les transactions observent les données modifiées par d'autres, équilibrant intégrité et concurrence.
Les niveaux d'isolation régissent l'interaction des transactions concurrentes. Les quatre niveaux ANSI sont : READ UNCOMMITTED (lectures sales), READ COMMITTED (évite les sales), REPEATABLE READ (données stables) et SERIALIZABLE (exécution sérielle). Chacun fait un compromis entre concurrence et cohérence. Les systèmes MVCC utilisent des instantanés pour des lectures non bloquantes.
graph LR
Center["Niveaux d'Isolation des Transactions"]:::main
Rel_transaction["transaction"]:::related -.-> Center
click Rel_transaction "/terms/transaction"
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classDef child fill:#0f172a,stroke:#10b981,color:#94a3b8,rx:5,ry:5;
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❓ Questions fréquentes
What is a dirty read?
Reading data that has been modified but not yet committed by another transaction.
What is a non-repeatable read?
Reading the same data twice within a single transaction yields different results because another transaction committed changes in between.
What is a phantom read?
A new row matching a query appears in subsequent reads within the same transaction, due to inserts by other transactions.
Which isolation level prevents dirty reads?
READ COMMITTED or SERIALIZABLE (and REPEATABLE READ) prevent dirty reads.
How should I choose an isolation level?
Base the choice on the required balance between correctness guarantees and concurrency, adjusting per operation, and consider MVCC or locking behavior of your DBMS.