What are the different transaction isolation levels in SQL?

What are the different transaction isolation levels in SQL?

In SQL, there are four main transaction isolation levels: Read Uncommitted, Read Committed, Repeatable Read, and Serializable. Each level defines how transaction integrity is visible to other transactions.

Can you explain each isolation level with examples?

Sure!

1. Read Uncommitted: Allows dirty reads. For example, if Transaction A updates a record, Transaction B can read that uncommitted data.
2. Read Committed: Prevents dirty reads. Transaction B can only read committed data from Transaction A.
3. Repeatable Read: Ensures that if Transaction B reads a record, it will see the same data if it reads it again, even if Transaction A modifies it.
4. Serializable: The strictest level, it ensures complete isolation from other transactions, making it appear as if transactions are executed one after another.

What are the trade-offs of using higher isolation levels?

Higher isolation levels provide more consistency but can lead to increased locking and reduced concurrency, which may impact performance. For example, Serializable can prevent other transactions from accessing data, leading to potential bottlenecks.

Which isolation level is generally recommended?

It depends on the application requirements. For most applications, Read Committed is a good balance between consistency and performance. However, if data integrity is critical, Serializable may be necessary.