Mitigate the impact of dirty reads in a distributed database

Official answer

A dirty read observes another transaction's uncommitted changes. It differs from reading an older committed value on a replica or seeing a committed value change between two statements.

Choose the engine's isolation/read contract that excludes uncommitted data. SQL Read Committed excludes dirty reads; stricter isolation may be needed for other invariants, but Serializable is not required solely for this issue. Serializable means committed results are equivalent to some serial order, not that transactions literally run one at a time. Applications may need to retry serialization failures.

In PostgreSQL, even Read Uncommitted behaves as Read Committed. If session A changes a row but has not committed, an ordinary Read Committed SELECT in session B sees the prior committed version. After A commits, a later statement in B may see the change. The latter behavior is not a dirty read.

For a distributed engine, check transaction scope, replica-read policy and cross-region guarantees independently. A version-checked update addresses lost updates; it is not by itself an isolation protocol preventing dirty reads. Consistent hashing controls key placement and movement, not transaction visibility or consistency.

Reproduce the claimed anomaly with two sessions and explicit begin/commit/rollback points. Choose the weakest contract that satisfies the actual invariant, then test concurrent reads, failure and retry behavior under the documented engine/version.