Can you list different levels of transaction isolation in databases and explain their differences?

There are several standard levels of transaction isolation in databases, which determine how and when changes made by one transaction become visible to others. The main levels of isolation:

1. Read Uncommitted

   • A transaction can see changes made by other transactions even if they are not yet committed.
   • Dirty reads are possible.

2. Read Committed

   • A transaction only sees changes that have been committed.
   • It prevents dirty reads but allows non-repeatable reads.

3. Repeatable Read

   • Guarantees that if data was read in a transaction, it will not change upon re-reading.
   • It prevents non-repeatable reads but allows phantom reads.

4. Serializable

   • The strictest level of isolation.
   • Transactions are executed as if they were executed sequentially, one after another.
   • It prevents phantom reads and provides full isolation.

Choosing an isolation level affects performance and data integrity: stricter levels ensure greater integrity but may reduce concurrency and increase locking.