Transaction isolation is one of the foundations of database processing. Isolation is the I in the acronym ACID; the isolation level is the setting that fine-tunes the balance between performance and reliability, consistency, and reproducibility of results when multiple transactions are making changes and performing queries at the same time.
Although some database management systems offer MVCC, usually concurrency control is achieved through locking. But as we all know, locking increases the serializable portion of the executed code, affecting parallelization.
The SQL standard defines four Isolation levels:
