What difficulties can arise from incorrect transaction isolation level settings?

Incorrectly defining the transaction isolation level can lead to several problems:

• Dirty Read: a transaction reads data that has been modified but not yet committed by another transaction. If that transaction rolls back, the data will be incorrect.
• Non-repeatable Read: when reading the same data multiple times within a transaction, the data may change if another transaction has updated it.
• Phantom Read: when executing the same query again within a transaction, new rows added by other transactions may appear.

If the isolation level is too low (e.g., READ UNCOMMITTED), the risk of these problems increases, which can lead to data inconsistency. If it is too high (e.g., SERIALIZABLE), it can cause locking and reduce performance due to resource contention.

Therefore, it is important to choose an isolation level that balances data integrity and performance.