Transaction Management

Question

Which of the following protocols does not ensure conflict serializability and safety from deadlocks?

1. Graph based protocols
2. Two-phase locking protocol
3. Time-stamp ordering protocol
4. Both a & b

Comments

don't know about graph based protocols but 2PL ensures conflict serializability but don't guarantee about deadlock free transaction and Time stamp protocol ensures both deadlock free transaction as well as conflict serializability.

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The Main Question is about Graph Based protocol, There is no explicit mention about it

Answer 1

Graph based protocols and timestamp ordering protocols ensure both conflict serializability and free from deadlocks.

But 2-phase locking protocol ensures only conflict serializability but not free from deadlocks

Comments

Provide some source or a definite proof behind your comment about graph based protocol. 

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In graph based protocols ,we  are restricted to use only rooted trees and exclusive locks only.

It is also called tree protocol , it works as

 Each transaction Ti can lock a data item at most once, and must observe the following
rules:
1. The first lock by Ti may be on any data item.
2. Subsequently, a data item Q can be locked by Ti only if the parent of Q is
currently locked by Ti .
3. Data items may be unlocked at any time.
4. A data item that has been locked and unlocked by Ti cannot subsequently
be relocked by Ti .

So, we cant get deadlocks here.

Since here if we want to access an element in the tree ,it has to follow the order from parent or root down to the leaf

Suppose in this graph if you have locked first on D and then you want to lock H and I.deadlock may possible if some transaction has  already locked H or J and waiting for D.

But this will not happen since they follow the order from root to the leaf So any transaction requests the locks in that order and deadlocks cannot happen