2 Phase Locking

Question

State True or False and Tell reason

1) 2PL is always conflict serializable

2)Timestamp protocol is conflict and view serializable

Answer 1

1.2PL ensures serial schedule, and every serial schedule is conflict serializable.

2. Timestamp ensures conflict serializable schedule and every conflict serializable schedule is view serializable.

Both options are true.

Comments

but is every 2PL is serializable or strict 2PL is serializable?

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every 2pl guarantee serializbilty because a 2pl has two phase growing and shrinking ,so once it has released a lock it will not ask for again. 

maybe it will help:https://en.wikipedia.org/wiki/Two-phase_locking

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Strict 2PL is to ensure cascadeless schedules and recoverability

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Every 2PL is serializable ? view serializable schedule is guarantee for serializability and so the question eventually is Every 2PL is view serializable , yes! when conflict serializable then view serializable.

Strict 2PL , is an update of 2PL to ensure recoverability , it's no where related to serializability.BUt as our 2PL ensures serializability so yes strict 2PL is not only serializable but recoverable too.

useful references

http://www.edugrabs.com/2-phase-locking/

http://www.edugrabs.com/timestamp-ordering-protocols/

http://www.edugrabs.com/serializability-in-database/

Answer 2

1.  2PL is always conflict serializable 

This is True because the basic motive of 2 phase locking is to ensure serializability because binary locks or shared and exclusive locks in transaction does not guarantee serializability of schedules on its own.

• 2 phase locking always results in conflict serializable schedule.
• But every conflict serializable schedule does not ensure it can satisfy 2 phase locking

2. Timestamp protocol is conflict and view serializable

• Every schedule satisying Timestamp protocol is conflict serializable and hence view serializable

Comments

@Mk Utkarsh

If we have schedule that does locking in 2PL..

But leading to deadlock ...then will that schedule be conflict serializable??