Final answer:
The answer to complete the given sentence is 'redo.' This term is used within the context of database recovery mechanisms to describe the process of applying transaction changes from the log to the database after a failure.
Step-by-step explanation:
We can complete the sentence as follows: We can also redo the effect of the write operations of a transaction T by tracing forward through the log and setting all items changed by a write operation of T (that did not get done permanently) to their new_values.
This process is part of a recovery mechanism in database systems, ensuring that despite any failures, the database can be restored to a consistent state. The redo operation is used during recovery to apply all the changes that a transaction T has made to the database but which were not permanently written to disk before a system failure occurred. This is typically achieved by going through the log, which is a record of all transactions and their respective write operations, and redoing every write operation for the affected items.
We can also undo the effect of the write operations of a transaction T by tracing forward through the log and setting all items changed by a write operation of T (that did not get done permanently) to their new values.
In the context of database transactions and recovery mechanisms, the term "undo" refers to the process of reversing the changes made by a transaction that was not committed successfully. This helps maintain the consistency and integrity of the database, especially in the case of system failures or unexpected shutdowns. The log plays a crucial role in recording the sequence of operations and their effects, allowing for recovery procedures such as undo to be applied when needed.