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Solution to Previous Year Exam Questions for Database Management System - DBMS of WBUT by Rashbihari Halder

by Rashbihari Halder
Type: PYQ SolutionInstitute: West Bengal University of technology Course: B.Tech Specialization: Computer Science EngineeringOffline Downloads: 43Views: 1325Uploaded: 10 months agoAdd to Favourite

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Database Management System by Rashbihari Halder

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ENGINEERING & MANAGEMENT EXAMINATIONS, DECEMBER – 2008 DISTRIBUTED DATABASE SEMESTER – 7 2. Explain 3-phase commit protocol. Ceri Page no 251 Why is it non-blocking ? The new protocol allows termination for all failures during the second phase which blocked the standard 2-phase protocol; however, we must show that blocking cannot occur because of a failure during the third additional phase which has been added. This is simple, because all participants are in the prepared-to-commit state when this phase begins. Hence the termination protocol will elect a new coordinator and commit the transaction in case of failure of the original coordinator. The new protocol requires three phases for committing a transaction and two phases for aborting it. Several termination protocols for operational participants and restart protocols for failed participants can be designed to operate correctly with the 3-phasecommitment protocol. 3. Describe catalogue management in distributed database systems. Ceri Page no: 278 i.e - CATALOG MANAGEMENT IN DISTRIBUTED DATABASE and CONTENTS OF CATALOG 4. What is false deadlock ? How is it overcome ? Ceri Page No: 225 5. Differentiate between distributed database and parallel database. Parallel Database A parallel database system is one that seeks to improve performance through parallel implementation of various operations such as loading data, building indexes, and evaluating queries. Although data may be stored in a distributed fashion in such a system, the distribution is governed solely by performance considerations.
Parallel database Architecture  Three main architectures have been proposed for building parallel DBMSs.  In a shared-memory system, multiple CPUs are attached to an interconnection network and can access a common region of main memory.  In a shared-disk system, each CPU has a private memory and direct access to all disks through an interconnection network.  In a shared-nothing system, each CPU has local main memory and disk space, but no two CPUs can access the same storage area; all communication between CPUs is through a network connection. Distributed database: A distributed database (DDB) is a collection of multiple, logically interrelated databases distributed over a computer network. A distributed database management system (D–DBMS) is the software that manages the DDB and provides an access mechanism that makes this distribution transparent to the users. A number of autonomous processing elements (not necessarily homogeneous) that are interconnected by a computer network and that cooperate in performing their assigned tasks. 6. What is join graph ? What are the different types of a join graphs ? Indicate briefly the use of join graphs in distributed database systems. Ceri Page No: 78
7. a) What do you mean by simplification of joins between horizontally Fragmented relations ? Explain with an example. Ceri Page No: 108 – 110. Define the term "Qualified Relation". Ceri Page No: 103 Prove that R IN S = S IN R using R IN S = R DF ( R DF S ). Describe the simplification of horizontally fragmented relations using an example. Ceri Page No: 108 8. a) What are the methods to prevent unauthorized users in remote accessing in distributed database ? Ceri Page No: 283 b) Explain the concurrency control mechanisms ? Ceri Page No: 213 Concurrency Control Concurrency control is the problem of synchronizing concurrent transactions (i.e., order the operations of concurrent transactions) such that the following two properties are achieved: – the consistency of the DB is maintained – the maximum degree of concurrency of operations is achieved Obviously, the serial execution of a set of transaction achieves consistency, if each single transaction is consistent. Concurrency control mechanism are of two types ; optimistic method and pessimistic method Pessimistic methods assume that many transactions will conflict, thus the concurrent execution of transactions is synchronized early in their execution life cycle  Two-Phase Locking (2PL)  Centralized (primary site) 2PL  Primary copy 2PL  Distributed 2PL
 Timestamp Ordering (TO)  Basic TO  Multiversion TO  Conservative TO  Hybrid algorithms Optimistic methods assume that not too many transactions will conflict, thus delay the synchronization of transactions until their termination  Locking-based  Timestamp ordering-based 9. What is the blocking problem in 2-phase commit protocol ? A problem with the basic 2-phase-commitment protocol is that a subtransaction which has entered its ready state could be blocked A typical reason for blocking is a failure of the coordinator or of the communication network. The blocked subtransactions must keep all their resources until they receive the final command during the recovery from the failure, because they must be able of eventually committing or aborting. Therefore blocking reduces the availability of the system in case of failures. Explain how does 3-phase commit overcome this problem. The new protocol allows termination for all failures during the second phase which blocked the standard 2-phase protocol; however, we must show that blocking cannot occur because of a failure during the third additional phase which has been added. This is simple, because all participants are in the prepared-to-commit state when this phase begins. Hence the termination protocol will elect a new coordinator and commit the transaction in case of failure of the original coordinator. The new protocol requires three phases for committing a transaction and two phases for aborting it. Several termination protocols for operational participants and restart protocols for failed participants can be designed to operate correctly with the 3-phasecommitment protocol. Describe the distributed deadlock detection algorithm with an example. Ceri Page No: 223 and 224

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