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 has which of the following advantages over a centralized database?

Correct answer: Modular growthA distributed system can be extended by adding a site, without replacing or resizing a central machine, so capacity grows in steps matched to demand. The other three options are the recognised disadvantages: the software costs more, is more complex, and can respond more slowly where a query has to reach several sites.

Q: A transaction manager is which of the following?

Correct answer: All of the above.The transaction manager is responsible for atomicity and isolation, so it must log what each transaction does, hold the before and after images needed to undo or redo it, and apply the concurrency control that keeps concurrent transactions from interfering. All three are aspects of the same duty.

Q: Location transparency allows for which of the following?

Correct answer: All of the above.Location transparency means nobody has to know where the data physically sits - not the user writing a query, not the programmer writing an application, not the manager reading a report. The system resolves the location, which is what allows data to be moved between sites without changing anything above.

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.

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 has which of the following advantages over a centralized database?

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

Answer: D

Correct answer: Modular growth

A distributed system can be extended by adding a site, without replacing or resizing a central machine, so capacity grows in steps matched to demand. The other three options are the recognised disadvantages: the software costs more, is more complex, and can respond more slowly where a query has to reach several sites.

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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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A transaction manager is which of the following?

A.Maintains a log of transactions
B.Maintains before and after database images
C.Maintains appropriate concurrency control
D.All of the above.

Answer: D

Correct answer: All of the above.

The transaction manager is responsible for atomicity and isolation, so it must log what each transaction does, hold the before and after images needed to undo or redo it, and apply the concurrency control that keeps concurrent transactions from interfering. All three are aspects of the same duty.

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Location transparency allows for which of the following?

A.Users to treat the data as if it is at one location
B.Programmers to treat the data as if it is at one location
C.Managers to treat the data as if it is at one location
D.All of the above.

Answer: D

Correct answer: All of the above.

Location transparency means nobody has to know where the data physically sits - not the user writing a query, not the programmer writing an application, not the manager reading a report. The system resolves the location, which is what allows data to be moved between sites without changing anything above.

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A heterogeneous distributed database is which of the following?

A.The same DBMS is used at each location and data are not distributed across all nodes.
B.The same DBMS is used at each location and data are distributed across all nodes.
C.A different DBMS is used at each location and data are not distributed across all nodes.
D.A different DBMS is used at each location and data are distributed across all nodes.

Answer: D

Correct answer: A different DBMS is used at each location and data are distributed across all nodes.

Heterogeneous means the sites run different products, and the difficulty is exactly that: differing SQL dialects, data types, transaction models and catalogue structures must be reconciled before a single query can span them. Homogeneity is easier to manage but is often not available, since sites arrive through acquisition and separate history.

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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.

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10.

Which of the following is true concerning a global transaction?

A.The required data are at one local site and the distributed DBMS routes requests as necessary.
B.The required data are located in at least one nonlocal site and the distributed DBMS routes requests as necessary.
C.The required data are at one local site and the distributed DBMS passes the request to only the local DBMS.
D.The required data are located in at least one nonlocal site and the distributed DBMS passes the request to only the local DBMS.

Answer: B

Correct answer: The required data are located in at least one nonlocal site and the distributed DBMS routes requests as necessary.

A transaction is global when it needs data from beyond its own site, and the distributed DBMS then decomposes it and routes the pieces to wherever the data lives. A local transaction is satisfied entirely at one site and needs no such routing - the distinction that decides how much coordination the transaction costs.

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