Can you explain what the transaction isolation level means in a database management system?

The transaction isolation level in a DBMS determines how much a transaction can see the changes made by other concurrent transactions. This is important for preventing data integrity issues such as:

• Dirty Read — reading uncommitted changes made by another transaction.
• Non-repeatable Read — when data changes between two reads within the same transaction.
• Phantom Read — the appearance of new rows matching the query condition between two reads.

Main isolation levels:

• Read Uncommitted — the lowest level, allows dirty reads.
• Read Committed — prevents dirty reads but allows non-repeatable reads.
• Repeatable Read — prevents non-repeatable reads.
• Serializable — the strictest level, provides full isolation as if transactions are executed sequentially.

Choosing an isolation level is a trade-off between performance and data integrity.