What are the disadvantages of two-phase locking?
- Produced schedule through 2PL locking may be irrecoverable.
- Produced schedule through 2PL locking may contains a deadlock problem.
- Produced schedule through 2PL locking may contains a Starvation Problem.
- Cascading Rollback Problem.
If a thread holding a lock is permanently blocked (due to an infinite loop, deadlock, livelock, or other liveness failure), any threads waiting for that lock can never make progress. Even ignoring these hazards, locking is simply a heavyweight mechanism for fine-grained operations such as incrementing a counter.
Two-phase locking may also limit the amount of concurrency that occurs in a schedule because a Transaction may not be able to release an item after it has used it. This may be because of the protocols and other restrictions we may put on the schedule to ensure serializability, deadlock freedom, and other factors.
Every transaction will lock and unlock the data item in two different phases. Growing Phase − All the locks are issued in this phase. No locks are released, after all changes to data-items are committed and then the second phase (shrinking phase) starts.
Two transactions cannot have conflicting locks. No unlock operation can precede a lock operation in the same transaction. No data are affected until all locks are obtained—that is, until the transaction is in its locked point.
AdvantagesRecovery is very easy. DisadvantagesConcurrency is reducedExplain time stamp based protocol. Time stamp based protocolThis protocol uses either system time or logical counter to be used as a time-stamp.
Answer: Locking has a poor degree of concurrency. It in fact has no concurrency at all.
Two Phase Locking Protocol also known as 2PL protocol is a method of concurrency control in DBMS that ensures serializability by applying a lock to the transaction data which blocks other transactions to access the same data simultaneously. Two Phase Locking protocol helps to eliminate the concurrency problem in DBMS.
Two-Phase Locking (2PL) is a concurrency control method which divides the execution phase of a transaction into three parts. It ensures conflict serializable schedules. If read and write operations introduce the first unlock operation in the transaction, then it is said to be Two-Phase Locking Protocol.
What rule applies to the two-phase locking protocol? Two transactions cannot have conflicting lock.
Which of the following is true about two-phase locking?
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201.
| (a) | Heap file organization |
|---|---|
| (b) | Sequential file organization |
| (c) | Clustering file organization |
| (d) | Hash file organization |
| (e) | Index file organization. |
Two phase locking prevents deadlock from occuring in distributed systems by releasing all the resources it has acquired, if it is not possible to obtain all the resources required without waiting for another process to finish using a lock.
Although two-phase locking guarantees serializability, another problem called a deadlock can occur. A deadlock occurs during two-phase locking when a transaction is waiting for an item that is locked exclusively by another.
The central locking system is a very important line of safety for the occupants of the car. Each car key has a distinct code that synchronises with the alarm system of the vehicle. Once the car is locked using the key, the engine immobiliser goes off.
A lock is a mechanism used to synchronize different processing threads, with set limits to avoid unlimited accessibility of a certain resource within a computing environment. It is a method meant to arrange access by applying simultaneous control policies.
