conservative two phase locking protocol

Question

Does the conservative two phase locking protocol produce cascadeless schedules?

Let us consider the following schedule :

Since in the schedule the lock on a is released, it is possible for the transaction T2 to acquire the lock on a. Now the transaction T2 reads the value of a which was written by transaction T1. This implies that if the transaction T1 aborts, the transaction T2 must be aborted for consistency purposes. Does it mean that even though a conservative two phase protocol is used, the schedules may not necesssarily be cascadeless?

Answer 1

Conservative 2 PL: A transaction has to lock all the items it access before the transaction begins execution. It helps to prevent deadlock but not starvation and cascading rollbacks.

Whatever you said above is correct, Conservative 2 PL doesn't prevent Cascading rollbacks while Strict 2PL/ Rigorous 2PL does.

Comments

is there any comparison between conservative 2PL , Strict 2PL, Basic 2PL and Rigorous 2PL,like conflict and view serializable

---

i think there is no comparison between conservative 2pl and remaining 2pl protocol but we can say that every rigorous 2l is strict(there is chance of deadlock but must prevent cascading rollback)

confirm this pls?

---

strict 2pl and rigorous 2pl doesnt have cascading rollbacks  but have deadlock

conservative 2pl has no deadlock problem but has cascading rollbacks problem

---

strict 2pl and rigorous 2pl have deadlock problem and no cascading rollback problem as all exclusive locks are hold until commit so rollback problem is avoided here in case of conservative 2pl all locks are acquired before beginning of transaction no acquisition in between transaction therefore no deadlock but rollback problem still is there