Explain deadlock and starvation. Explain Time stamp based protocol for concurrency control?

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Suresh Chand · Accepted Answer

Starvation: Starvation is the situation when a transaction has to wait for an indefinite period of time to acquire a lock. Reasons for Starvation: If the waiting scheme for locked items is unfair. ( priority queue ) Victim selection (the same transaction is selected as a victim repeatedly ) Resource leak. Via denial-of-service attack. Solution: Increasing Priority Modification in Victim Selection algorithm First Come First Serve approach Wait-die and wound wait scheme Deadlock: Deadlock means that there is a set of two or more transactions that are all stuck because they are all waiting for locks to be released that have been acquired earlier by one of the other transactions in the set. Note that this means that none of the transactions can therefore ever make progress. It also means that assuming that transactions follow a protocol like two-phase locking to guarantee serializability, this cannot be resolved by some transaction releasing a lock, but only by aborting one or more of the transactions. A typical example is where transaction T1 is holding a lock on record r1 and is requesting a lock on record r2, and transaction T2 is holding a lock on record r2 and requesting a lock on record r1. If neither transaction will release the locks they already have, this means that both T1 and T2 are stuck. Timestamp-based protocol for concurrency control: The most commonly used concurrency protocol is the timestamp-based protocol. This protocol uses either system time or a logical counter as a timestamp. Lock-based protocols manage the order between the conflicting pairs among transactions at the time of execution, whereas timestamp-based protocols start working as soon as a transaction is created. Every transaction has a timestamp associated with it, and the ordering is determined by the age of the transaction. A transaction created at 0002 clock time would be older than all other transactions that come after it. For example, any transaction 'y' entering the system at 0004 is two seconds younger and the priority would be given to the older one. In addition, every data item is given the latest read and write timestamp. This lets the system know when the last ‘read and write operation was performed on the data item.

Explain deadlock and starvation. Explain Time stamp based protocol for concurrency control?

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Explain deadlock and starvation. Explain Time stamp based protocol for concurrency control?

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