Choosing a Postgres isolation level for read-heavy APIs

Knowledge base / Databases

Databases · published 2026-09-04 · #postgres#transactions#isolation-levels

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Problem

APIs backed by Postgres often read data that must be internally consistent within a single request, without paying the cost of serializable transactions.

Solution

Use READ COMMITTED for most endpoints and switch to REPEATABLE READ only for transactions that need a stable snapshot across several queries.

Caveats

REPEATABLE READ in Postgres can fail with serialization errors that the application must retry.