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Snapshot Isolation

An isolation level providing a consistent view of the database at a specific point in time, minimizing blocking.
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The statement of the theorem

Let DD be the database state and TstartT_{start} be the timestamp defining the snapshot. Define the read operation Read(d,Tstart)\text{Read}(d, T_{start}) such that it retrieves the version of data item dd whose commit timestamp TScommit(d)\text{TS}_{\text{commit}}(d) satisfies TScommit(d)≤Tstart\text{TS}_{\text{commit}}(d) \le T_{start} and TScommit(d)\text{TS}_{\text{commit}}(d) is maximized. This ensures that all reads within the transaction view are consistent with the state at TstartT_{start}, effectively isolating the transaction from concurrent writes that commit after TstartT_{start}.