Zybook 4-2 Flashcards
(27 cards)
X Y Z
9 4 0
After Schedule executes, what is the value of Z?
3
X Y Z
9 4 0
After Equivalent Schedule executes, what is the value of Z?
3
X Y Z
9 4 0
After Conflicting Schedule executes, what is the value of Z?
2
X Y Z
9 4 0
The __________ Schedule has the same result as Schedule.
Equivalent
X Y Z
9 4 0
The ___________ Schedule has a different result than Schedule.
Conflicting
schedule in which transactions are executed one at a time. ————- have no concurrent transactions.
serial schedule
can be transformed into a serial schedule by switching the relative order of reads in different transactions
serializable schedule
A SERIALIZABLE transaction can run concurrently with a READ COMMITTED transaction.
True
When two READ UNCOMMITTED transactions run concurrently, the result may vary.
True
Transactions A and B are both SERIALIZABLE, and A always starts before B. The result may vary.
False
Transaction A writes data and rolls back before transaction B reads the data.
Strict
Transaction A writes data. Transaction B reads the data and commits before transaction A commits.
Nonrecoverable
Transaction A writes data. Transaction B reads the data. Transaction A rolls back before B commits.
Cascading
Several transactions can hold concurrent shared locks on the same row.
True
Several transactions can hold concurrent exclusive locks on the same row.
False
One transaction can hold an exclusive lock while other transactions hold shared locks on the same row.
False
Several transactions can hold concurrent exclusive locks on the same block, as long as the transactions access different rows in the block.
False
When a transaction takes a shared lock on a block, other transactions may be delayed.
True
Which two-phase locking technique results in the longest wait times for concurrent transactions?
Rigorous
Which two-phase locking technique has, in effect, just one phase?
Rigorous
A database uses basic two-phase locking. Transaction A takes an exclusive lock on X. Transaction B requests a shared lock on X. When is the shared lock granted?
During the contract phase of A
A database uses strict two-phase locking. Transaction A takes an exclusive lock on X. Transaction B requests a shared lock on X. When is the shared lock granted?
After A commits or rolls back
Refer to the above animation. How many transactions must roll back to break the deadlock?
One
Whenever deadlock occurs, a cycle of dependent transactions always exists.
True
