What does the isolation level Read Committed mean and how does it ensure data integrity during concurrent transactions?

The Read Committed isolation level guarantees that a transaction only sees data that has been committed by other transactions. This prevents dirty reads, where one transaction reads data modified but not yet committed by another.

How it works:

• When reading data, a transaction only sees changes that were committed before the start of the read.
• If another transaction has not yet committed its changes, those changes will not be visible.

Thus, Read Committed ensures data integrity by preventing the reading of uncommitted, intermediate changes. However, phenomena like non-repeatable reads can occur, where a repeated query within the same transaction may return different data if another transaction modifies and commits data between reads.

Example:

• Transaction A reads a record.
• Transaction B modifies and commits that record.
• If Transaction A reads again, it will see the updated data.

This is normal behavior for Read Committed, balancing performance and data integrity.