Distributed Databases Questions and Answers

Q: An advantage of distributed database over a centralized database :

An advantage of a distributed database is modular growth.A distributed database can be expanded by adding new sites or nodes, each with its own processing and storage, without disturbing the rest of the system. A centralised system must instead be upgraded as a whole.Higher software cost and greater software complexity are disadvantages of distributed databases, because of distributed query processing, concurrency control and recovery. Slow response is not an advantage either; local access is usually faster.

Q: Which protocol ensures that mobile hosts can participate in transactions with minimal blocking during disconnections ?

The answer is proxy-based commit.Mobile hosts disconnect often, voluntarily or not. In proxy-based commit schemes for mobile transactions, an agent on the fixed network acts for the mobile host in the commit protocol, keeping its vote and state, so the other participants are not left waiting with locks held while the mobile host is out of contact.Standard two-phase commit is a blocking protocol: a participant that has voted to commit must wait for the coordinator's decision, and an unreachable participant holds everyone up. Presumed commit is an optimisation of 2PC that saves log writes and messages by assuming commit when no record is found; it does not remove the blocking. Since one listed protocol fits, 'None of these' is wrong.

Q: Which of the following is a disadvantage of a centralized database ?

A disadvantage of a centralised database is that it may lead to a single point of failure.All data is held at one site, so if that server or its network link fails, every user loses access, and a disaster there can lose the data unless backups exist.Better security through limited access and real-time consistency are advantages of centralisation, and scaling a single central server is harder, not easier.

Q: A distributed database can use which of the following strategies?

Correct answer: All of the aboveAll three are legitimate distribution strategies, chosen according to where the data is used. Centralised suits a system with one authoritative source; replication suits read-mostly data needed everywhere; and partitioning suits data naturally divided by site, such as regional customers. Most real systems combine them.

Q: Storing a separate copy of the database at multiple locations is which of the following?

Correct answer: Data ReplicationReplication stores a full copy at each of several sites, so every query can be answered locally and the failure of one site does not stop the others. The cost is keeping the copies consistent, which is why it suits data that is largely read and rarely changed.

Q: Some of the columns of a relation are at different sites is which of the following?

Correct answer: Vertical PartitioningVertical partitioning divides a relation by column, keeping the primary key with each fragment so the original can be reconstructed by a join. It suits a case where different sites use different attributes of the same entity - personnel data at one site and payroll data at another, for the same employees.

Q: The semijoin approach saves network traffic.

Correct answer: TrueThe semijoin sends only the joining column values out and receives only the matching rows back, so both directions carry far less than a full transfer of either table. Where the network is the bottleneck - which in a distributed database it usually is - that saving governs the cost of the query.

Q: Replication may use either synchronous or asynchronous distributed database technologies, although asynchronous technologies are more typical in a replicated environment.

Correct answer: TrueSynchronous replication updates every copy within the same transaction, which guarantees consistency but makes the transaction depend on every site being available. Asynchronous replication propagates changes afterwards, accepting a period of inconsistency in exchange for availability and speed, and that trade is the one usually taken.

An advantage of distributed database over a centralized database :

A.Modular growth
B.Software cost
C.Software complexity
D.Slow response

Exam Year(s)

MH SET - 2024, SET Exam - 2024,

Answer: A

An advantage of a distributed database is modular growth.

A distributed database can be expanded by adding new sites or nodes, each with its own processing and storage, without disturbing the rest of the system. A centralised system must instead be upgraded as a whole.

Higher software cost and greater software complexity are disadvantages of distributed databases, because of distributed query processing, concurrency control and recovery. Slow response is not an advantage either; local access is usually faster.

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Which protocol ensures that mobile hosts can participate in transactions with minimal blocking during disconnections ?

A.Presumed commit
B.Two-phase commit
C.Proxy-based commit
D.None of these

Exam Year(s)

Tripura Public Service Commission - 2026,

Answer: C

The answer is proxy-based commit.

Mobile hosts disconnect often, voluntarily or not. In proxy-based commit schemes for mobile transactions, an agent on the fixed network acts for the mobile host in the commit protocol, keeping its vote and state, so the other participants are not left waiting with locks held while the mobile host is out of contact.

Standard two-phase commit is a blocking protocol: a participant that has voted to commit must wait for the coordinator's decision, and an unreachable participant holds everyone up. Presumed commit is an optimisation of 2PC that saves log writes and messages by assuming commit when no record is found; it does not remove the blocking. Since one listed protocol fits, 'None of these' is wrong.

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Which of the following is a disadvantage of a centralized database ?

A.It can be more secure due to limited access.
B.It provides real-time data consistency.
C.It may lead to a single point of failure.
D.It can be easily scaled.

Exam Year(s)

Tripura Public Service Commission - 2025,

Answer: C

A disadvantage of a centralised database is that it may lead to a single point of failure.

All data is held at one site, so if that server or its network link fails, every user loses access, and a disaster there can lose the data unless backups exist.

Better security through limited access and real-time consistency are advantages of centralisation, and scaling a single central server is harder, not easier.

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A distributed database can use which of the following strategies?

A.Totally centralized at one location and accessed by many sites
B.Partially or totally replicated across sites
C.Partitioned into segments at different sites
D.All of the above

Answer: D

Correct answer: All of the above

All three are legitimate distribution strategies, chosen according to where the data is used. Centralised suits a system with one authoritative source; replication suits read-mostly data needed everywhere; and partitioning suits data naturally divided by site, such as regional customers. Most real systems combine them.

Discuss in Forum

Storing a separate copy of the database at multiple locations is which of the following?

A.Data Replication
B.Horizontal Partitioning
C.Vertical Partitioning
D.Horizontal and Vertical Partitioning

Answer: A

Correct answer: Data Replication

Replication stores a full copy at each of several sites, so every query can be answered locally and the failure of one site does not stop the others. The cost is keeping the copies consistent, which is why it suits data that is largely read and rarely changed.

Discuss in Forum

Some of the columns of a relation are at different sites is which of the following?

A.Data Replication
B.Horizontal Partitioning
C.Vertical Partitioning
D.Horizontal and Vertical Partitioning

Answer: C

Correct answer: Vertical Partitioning

Vertical partitioning divides a relation by column, keeping the primary key with each fragment so the original can be reconstructed by a join. It suits a case where different sites use different attributes of the same entity - personnel data at one site and payroll data at another, for the same employees.

Discuss in Forum

An autonomous homogenous environment is which of the following?

A.The same DBMS is at each node and each DBMS works independently.
B.The same DBMS is at each node and a central DBMS coordinates database access.
C.A different DBMS is at each node and each DBMS works independently.
D.A different DBMS is at each node and a central DBMS coordinates database access.

Answer: A

Correct answer: The same DBMS is at each node and each DBMS works independently.

Homogeneous means the same product at every site; autonomous means each site manages itself, with no central authority coordinating access. The combination is common where an organisation has standardised on one product but its sites were developed separately and retain local control.

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The semijoin approach saves network traffic.

A.True
B.False

Answer: A

Correct answer: True

The semijoin sends only the joining column values out and receives only the matching rows back, so both directions carry far less than a full transfer of either table. Where the network is the bottleneck - which in a distributed database it usually is - that saving governs the cost of the query.

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Replication may use either synchronous or asynchronous distributed database technologies, although asynchronous technologies are more typical in a replicated environment.

A.True
B.False

Answer: A

Correct answer: True

Synchronous replication updates every copy within the same transaction, which guarantees consistency but makes the transaction depend on every site being available. Asynchronous replication propagates changes afterwards, accepting a period of inconsistency in exchange for availability and speed, and that trade is the one usually taken.

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10.

Replication should be used when which of the following exist?

A.When transmission speeds and capacity in a network prohibit frequent refreshing of large tables.
B.When using many nodes with different operating systems and DBMSs and database designs.
C.The application's data can be somewhat out-of-date.
D.All of the above.

Answer: C

Correct answer: The application's data can be somewhat out-of-date.

Replication is asynchronous in practice, so copies lag behind one another between refreshes. That is acceptable only where the application can work with data a little out of date - a catalogue or a reference table rather than a live account balance. The other two options describe conditions in which replication should be avoided.

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Distributed Databases Questions and Answers

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