What are the levels of transaction isolation in database management systems?

In database management systems (DBMS), there are standard transaction isolation levels defined in the SQL standard that regulate the visibility of changes between transactions and prevent various anomalies:

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 by other transactions.
   • Prevents dirty reads, but non-repeatable reads are possible.

3. Repeatable Read

   • Ensures that data read in a transaction does not change until the transaction completes.
   • Prevents non-repeatable reads, but phantom reads are possible.

4. Serializable

   • The strictest isolation level.
   • Transactions are executed as if they were executed sequentially.
   • Prevents all types of anomalies, including phantom reads.

Each isolation level balances between performance and data consistency. The choice depends on the application's requirements and the capabilities of the DBMS.