Table of Contents

Snapshot isolation

In one line: every read sees a consistent view of the database frozen at the transaction's start — no locks, no waiting on writers.

Visibility is keyed on the TSN (Transaction Sequence Number), Typhon's visibility clock. A reader sees every change committed with TSN ≤ its own, plus its own uncommitted writes; it never sees anyone else's uncommitted writes, nor any commit that landed after it began. Readers never take a lock and never block a writer — the cost is keeping older versions around while someone might still need them.

Because the snapshot is fixed, this prevents dirty reads, non-repeatable reads, and phantoms — re-running a query inside one transaction never surfaces rows another transaction committed after your snapshot. It is still not serializable: the anomaly it permits is write skew — two transactions each read an overlapping set, then write disjoint items, together breaking an invariant that spans them. Only Versioned components get this; SingleVersion/Transient reads are live (the latest in-place value), with no isolation.

⚠️ "Point in time" here means your transaction's start — a consistent current view. It is not reading historical/past versions (Typhon has no user-facing as-of-past read API). Don't confuse it with PointInTimeAccessor, which is the same idea fanned across threads.

How it relates

In the API

Learn & use

Edit this page