What is the function of a database transaction log?

The function of a database transaction log is to record all changes made to a database for recovery in case of a failure. This is a critical component of database management systems because it ensures data integrity and durability. If a transaction is completed successfully, the log captures the change; if a failure occurs (such as a system crash or power loss), the transaction log allows for the database to be restored to a consistent state by replaying or rolling back transactions as necessary.

Through this logging mechanism, any updates, deletions, or insertions are noted, enabling the recovery process to either ensure that all transactions that were committed are fully applied or that any incomplete transactions are properly undone. This process is vital for maintaining reliable and consistent data in the event of unexpected issues.

Other options presented do not accurately reflect the primary purpose of a transaction log. While daily summaries and user access logs are useful for different aspects of database management—such as reporting and security—they do not provide the same level of transactional safety and recovery that the transaction log does. Performance tracking of database queries, while important for tuning and optimization, is not the role of the transaction log either. Thus, recording changes for recovery stands out as the core function.