What types of problems can occur in a database during concurrent processing of multiple transactions?

When processing multiple transactions simultaneously in a database, the following problems may occur:

• Dirty Read: one transaction reads data that has been modified but not yet committed by another transaction.
• Non-repeatable Read: when reading the same data again within a transaction, the data may change due to another transaction.
• Phantom Read: when re-executing a query within a transaction, new rows added by another transaction appear.
• Locks and Deadlocks: transactions may block each other, waiting for resources to be released.

To prevent these problems, transaction isolation levels are used, which regulate the visibility of changes between transactions and locking.