# How does transaction isolation affect what a database session can read?

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HELP CENTER · FAQ Databases 1 min read
# How does transaction isolation affect what a database session can read?
Transaction isolation controls how a transaction observes changes made by other concurrent transactions. The available levels and exact guarantees vary by database engine, so confirm the behavior for your engine and workload rather than relying on a level name alone.
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Databases

## Identify the anomaly you need to prevent
Consider whether the workflow must avoid dirty reads, nonrepeatable reads, or inconsistent ranges while another transaction writes. Stronger guarantees can require more locking or version tracking and may affect throughput or retry behavior.
Check whether the engine implements a level using locking, multiversion concurrency control, or engine-specific rules. Snapshot-based behavior may still allow anomalies such as write skew depending on the database and constraint design.
## Test the real transaction pattern
Use concurrent sessions that reproduce the application’s read and write order. Verify observed results under the configured isolation level and include deadlocks, serialization failures, and retry handling in the test.
Choose the weakest level that satisfies the business invariant, then enforce critical invariants with constraints or explicit locking where appropriate. Document assumptions so a future engine or configuration change is reviewed. [← Back to Databases FAQs](https://help.iagenify.com/faqs/databases)