What are the reasons for differences in transaction isolation levels and why are there so many?

Differences in transaction isolation levels are related to the balance between performance and data integrity. The main levels of isolation:

• Read Uncommitted — a transaction can see uncommitted changes from other transactions (dirty read).
• Read Committed — a transaction only sees committed data, preventing dirty reads.
• Repeatable Read — guarantees that data read in a transaction will not change until its completion, preventing non-repeatable reads.
• Serializable — the strictest level, providing full transaction isolation as if transactions were executed sequentially.

Reasons for multiple levels:

• Different applications require different levels of consistency and performance.
• Stricter isolation levels reduce concurrency and can lead to locking.
• The ability to choose allows optimizing system performance for specific tasks.

Thus, isolation levels provide flexibility in managing the balance between data correctness and operational efficiency.