A _____________ contains the changes that have been made to the database. The missing word is one of the following:
System log
checkpoint
rollback journal
transaction
Read the following sentences concerning transactions, which one is incorrect?
A transaction T reaches its checkpoint when all its operations that access the database have been executed successfully
The system log keeps track of all transaction operations that affect the values of database items. This information may be needed to recover from transaction failure.
Before a transaction reaches its commit point, any portion of the log that has not yet been written to the disk must now be written to it. This process is called force writing the log file before committing a transaction.
A checkpoint is a system log entry. It is written into the log periodically at that point when the system writes out to the database on disk the effect of all write operations of committed transaction. True or false?
True
False
Performing a checkpoint consists of a number of operations. The order of these operations is incorrect. Which operation takes place first of all?
Writing (force-writing) all modified database buffers of committed transactions out to disk
Suspending executions of transactions temporarily
Writing (force-writing) all log records in main memory out to disk
Writing a checkpoint record to the log
One of these sentences is incorrect: ‘undo’ should be replaced by ‘redo’ – which one?
If a transaction crash occurs, then the recovery manager may undo transactions (that is, reverse the operations of a transaction on the database).
The recovery manager will undo transactions when it examines a transaction’s log entry, and for every write_item(T, x, old_value, new_value) entry, the value of item x in the database is set to new_value.
The main technique used to handle catastrophic failure such as a disk crash is to redo the lost operations from the system log using the latest version of the database. True or False?
True
False
Deferred update technique for database recovery is also known as NO-UNDO/REDO; and immediate update technique is known as UNDO/REDO algorithm. True or False?
True
False
In deferred update protocol, a transaction cannot change the database until it reaches its commit point, neither should the changes be recorded in the transaction workspace. True or False?
True
False
In immediate update protocol, a transaction can update the database before it is committed, and the operations that change the database are force-writing to the database, therefore make it impossible for recovery if system failure occurs.True or False?
True
False
A common method of dealing with failures which do not affect the database (such as generation of reports) is to issue the commands that generate the reports but keep them as batch jobs. True or false?