A transaction’s isolation level changes what it can observe.

PostgreSQL offers isolation levels with different guarantees about concurrent work. At Read Committed, successive statements in one transaction can see different committed data. Stronger isolation can prevent additional anomalies, but applications must be prepared to retry transactions that fail with serialization errors. Choosing a level is part of designing application behavior.

PostgreSQL

Why it matters

Worth revisiting when concurrent requests update shared state, allocate resources, or make decisions from multiple reads.

More context

Write down the invariant the transaction must protect, then compare it with the documented behavior of the chosen isolation level. Test competing transactions rather than relying only on sequential examples. Keep retry logic outside the entire transaction boundary.

Keep in mind

Stronger isolation does not remove the need for constraints, careful transaction design, or handling retries.

Original read