Níveis de Isolamento de Transações
Regulam como as transações observam dados modificados por outras, equilibrando integridade com concorrência.
Os níveis de isolamento governam a interação de transações concorrentes. Os quatro padrões ANSI são: READ UNCOMMITTED (leituras sujas), READ COMMITTED (evita sujas), REPEATABLE READ (dados estáveis) e SERIALIZABLE (execução serial). Cada um troca concorrência por consistência. Sistemas MVCC usam snapshots para leituras sem bloqueio.
graph LR
Center["Níveis de Isolamento de Transações"]:::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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❓ Perguntas frequentes
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.