Distributed Database Question Bank with Answers Home

Question bank with answers on various topics of distributed database management systems, University exam questions with answers

Distributed Database (DDB) Question Bank Home

• Question bank SET 01

• Keywords: Homogeneous DDBS, Pipelined parallelism, Replication, Fragmentation, Deadlock detection, Transaparancies,  Autonomy - Definition, Comparison and more...

• Question bank SET 02

• Keywords: Distributed transactions, transparancies,  buffer coherency, global lock table, fragmentation vs replication

• Question bank SET 03

  • Keywords: Two Phase Commit (2PC), Parallel database architectures, types of replication, speed-up vs scale-up

• Question bank SET 04

  • Keywords: Inter-operation vs Intra-operation parallelism, parallel database, architectures in parallel database

• Question bank SET 05  

  • Keywords: optimal data allocation, derived horizontal fragmentation, correctness rules for horizontal and vertical fragmentation

• Question bank SET 06

• Question bank SET 07

• Question bank SET 08

• Question bank SET 09

• Question bank SET 10     

Distributed Database Question Bank with Answers 17

Distributed  and parallel database questions and answers for University exams

Question:

What is the major disadvantage of 2PC protocol? [Discuss the Blocking problem of 2PC]

Answer:

The major disadvantage of two phase commit protocol is Blocking problem.

Blocking problem – This happens is the transaction coordinator fails. In case of coordinator failure, 2PC uses various ways to complete the transaction (to abort or commit). It can be done using the messages found in the log files of participating sites. If all the participating sites have <ready T> message and no other control messages (such as <abort T> or <commit T>) then all the active sites which are participating in that transaction have to wait for their transaction coordinator to recover. This indefinite blocking with locks held is called blocking problem.

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Related Questions:

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• List all correctness criteria for vertical data fragmentation in distributed database.

• What is the goal of data allocation process when designing a distributed database? Discuss different criteria for “optimal” data allocation.

• List all correctness criteria for horizontal data fragmentation in distributed database.

• What is the relationship between semi-join and derived horizontal fragmentation?

Distributed Database Question Bank with Answers 17

Distributed  and parallel database questions and answers for University exams

Question:

Is there any relationship between semi-join computation and derived horizontal fragmentation? Justify your answer.

Answer:

Yes. Derived horizontal fragmentation is defined on the member relation of a link according to the selection operation defined on its owner, i.e. produces a fragment of the member relation which contains only tuples which are guaranteed to join with tuples in the owner relation (and satisfy some selection condition).

In a semijoin, say R ⋉ S, the joining column of s (owner) is sent over to r (member) to produce the horizontal fragment of r that is guaranteed to join with s. As a result, it retains all the correct tuples resulted in the join and only attributes of R.

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Related Questions:

• Go to Distributed Database Question Bank Home page
• Go to Distributed Database Quiz Questions Home page
• Go to Distributed Database Home page

• List all correctness criteria for vertical data fragmentation in distributed database.

• What is the goal of data allocation process when designing a distributed database? Discuss different criteria for “optimal” data allocation.

• List all correctness criteria for horizontal data fragmentation in distributed database.

• Discuss the major disadvantage of 2PC protocol, the 'Blocking problem'.

Distributed Database Question Bank with Answers 16

Distributed  and parallel database questions and answers for University exams

Question:

What is the goal of data allocation process when designing a distributed database? Discuss different criteria for “optimal” data allocation.

Answer:

• Reliability – more copies available in case of site crashes

• Increased performance for read-only queries

• Optimality may be defined in two ways: minimal cost and maximized performance.

• Minimal cost – cost of storing and querying a fragment at a site, cost of updating a fragment at all sites, cost of data communication

• Maximized performance – minimize query response time, maximize system throughput

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Related Questions:

• Go to Distributed Database Question Bank Home page
• Go to Distributed Database Quiz Questions Home page
• Go to Distributed Database Home page

• List all correctness criteria for horizontal data fragmentation in distributed database. 

• List all correctness criteria for vertical data fragmentation in distributed database.

• What is the relationship between semi-join and derived horizontal fragmentation?

• Discuss the major disadvantage of 2PC protocol, the 'Blocking problem'.

Distributed Database Question Bank with Answers 15

Distributed  and parallel database questions and answers for University exams

Question:

List all correctness criteria for vertical data fragmentation in distributed database. Explain the role of each of the listed conditions. 

Answer:

Completeness

Each attribute of the original relation MUST be assigned to one of the fragments; this is guaranteed by the PARTITION algorithm.

Reconstruction

Reconstruction is performed by the join operator. By joining all vertical fragments resulting from fragmentation of the original relation R, we MUST be able to get the original relation as the result.

Disjointness

The key attributes are replicated in each fragment in the case of vertical fragmentation, so the fragments are never ‘completely’ disjoint. However, they are considered to be disjoint if non-key attributes from the original relation R appear in only one fragment.

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Related Questions:

• Go to Distributed Database Question Bank Home page
• Go to Distributed Database Quiz Questions Home page
• Go to Distributed Database Home page

• List all correctness criteria for horizontal data fragmentation in distributed database.

• What is the goal of data allocation process when designing a distributed database? Discuss different criteria for “optimal” data allocation.

• What is the relationship between semi-join and derived horizontal fragmentation?

• Discuss the major disadvantage of 2PC protocol, the 'Blocking problem'.