What is the difference between the Read Committed and Read Uncommitted isolation levels in database management systems?

Transaction isolation levels determine how and when the changes made by one transaction become visible to other transactions.

• Read Uncommitted:

  • Allows transactions to read data that has been modified but not yet committed by other transactions.
  • This can lead to "dirty reads," where data may be rolled back later.
  • The lowest level of isolation, providing maximum concurrency but least reliability.

• Read Committed:

  • Transactions see only data that has been committed by other transactions.
  • Prevents dirty reads.
  • However, non-repeatable reads can occur, where data may change upon re-reading.

Example:

If transaction A modifies a row but has not yet committed, then:

• With Read Uncommitted, transaction B can read these changes.
• With Read Committed, transaction B will see the old value until transaction A commits.

Thus, Read Committed provides greater data integrity by limiting visibility to only committed changes.