Difference between Conservative and Rigorous 2-PL
Prerequisites – Two Phase Locking Protocol, and Categories of Two Phase Locking
1. Conservative 2-PL :
- It is also called as Static 2-PL.
- This protocol requires the transaction to lock all the items it access before the Transaction begins execution by pre-declaring its read-set and write-set.
- If any of the pre-declared items needed cannot be locked, the transaction does not lock any of the items, instead, it waits until all the items are available for locking.
2. Rigorous 2-PL :
- This requires that in addition to the lock being 2-Phase all Exclusive(X) and Shared(S) Locks held by the transaction be released until after the Transaction Commits.
- Rigorous is more restrictive than Strict 2-PL.
- The implementation of Rigorous 2-PL is easy.
Difference between Conservative and Rigorous 2-PL :
| S.No. | Conservative 2-PL | Rigorous 2-PL |
|---|---|---|
| 1. | A transaction has to acquire locks on all the data items it requires before the transaction begins it execution. | A transaction can acquire locks on data items whenever it requires (only in growing phase) during its execution. |
| 2. | It does not have a growing phase. | It has a growing phase. |
| 3. | It has a shrinking phase. | It does not have a shrinking phase. |
| 4. | It ensures that the schedule generated would be Serializable and Deadlock-Free. | It ensures that the schedule generated would be Serializable, Recoverable and Cascadeless. |
| 5. | It does not ensures Recoverable and Cascadeless schedule. | It does not ensures Deadlock-Free schedule. |
| 6. | It does not ensure Strict Schedule. | It ensures that the schedule generated would be Strict. |
| 7. | It is not used in practise as its difficult to implement. | It is easy to implement but a lighter version of it (i.e Strict 2-PL) is used in practise. |
| 8. | In Conservative 2-PL, a transaction can read a value of uncommitted transaction. | In Rigorous 2-PL, a transaction only reads value of committed transaction. |
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