Which of the following contains complete record of all activity that affected the contents of a database during a certain period of time?
ans is (a)
a transaction log is a history of actions executed by adatabase management system to guarantee ACID properties over crashes or hardware failures. Physically, a log is a file listing changes to the database, stored in a stable storage format.
If, after a start, the database is found in an inconsistent state or not been shut down properly, the database management system reviews the database logs foruncommitted transactions and rolls back the changes made by these transactions. Additionally, all transactions that are already committed but whose changes were not yet materialized in the database are re-applied. Both are done to ensure atomicity and durability of transactions.