Answer Posted / Priya Agarwal

"Informix supports four transaction isolation levels: READ UNCOMMITTED, READ COMMITTED, REPEATABLE READ, and SERIALIZABLE. Each level represents a trade-off between concurrency and consistency. Here is a brief explanation of each:nn1. READ UNCOMMITTED (U): This is the least restrictive isolation level, allowing uncommitted data changes to be visible to other transactions. Data can potentially be read in an inconsistent state.nn2. READ COMMITTED (RC): A transaction cannot see data that has not been committed by another transaction; however, a transaction can still see its own dirty reads, meaning it can see changes made by the transaction itself even before those changes are committed.nn3. REPEATABLE READ (RR): This level guarantees that a transaction will always see the same data for repeated reads, except for changes made by the transaction itself. It prevents dirty reads but allows phantom reads and non-repeatable reads.nn4. SERIALIZABLE (S): This is the highest isolation level, ensuring each transaction appears to execute serially, with no interference from other transactions. It completely eliminates phantom reads, non-repeatable reads, and dirty reads."

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