Snapshot isolation is a transaction isolation model in which a given transaction always sees the same, consistent state of the system representing the moment when a transaction has started. As a result, phenomena seen in certain other isolation levels (dirty, non-repeatable, and phantom reads) are avoided. Snapshot isolation is closely related to multiversion concurrency control.

Snapshot isolation is slightly weaker than the serializable isolation level available in some systems.

The main benefit of snapshot isolation is that, while providing a high transaction isolation level, it avoids locking for read operations. Such locks can be detrimental to database performance. By combining it with the optimistic concurrency control model, it allows Vector to achieve high performance of update operations without affecting the performance of read-only queries.

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