Quiz questions and answers in distributed database MCQ 08

Distributed database quiz questions with answers, MCQ in distributed database, solved exam questions in distributed database, distributed transaction processing, two phase commit protocol

Multiple Choice Questions with Answers in Distributed Database

Let us suppose that there are a transaction coordinator T_c and two participants P₁ and P₂. They are working on a transaction T₁.

[Refer here to understand more and to answer – 2PC protocol]

 

1. Which of the following will happen after the following sequence of events is completed as per Two Phase Commit (2PC) protocol?

T_C sends <Prepare T₁> to P₁ and P₂.

P₁ sends <Ready T₁> to T_C.

P₂ sends <Ready T₁> to T_C.

a) T_C sends <Commit T₁> to P₁.

b) T_C sends <Commit T₁> to P₂.

c) T_C sends <Abort T₁> to P₁.

d) T_C sends <Abort T₁> to P₂.

Answer: (a) TC sends <Commit T1> to P1 and (b) TC sends <Commit T1> to P2 It is given that the transaction coordinator sent a prepare message to all the participating sites and in-turn the participants responded with ready message. If all the participating sites are responded with ready message (these responses only known to coordinator at this moment), then the coordinator sends the commit message to all the participants.

 

2. Which of the following will happen after the following sequence of events is completed as per 2PC?

T_C sends <Prepare T₁> to P₁ and P₂.

P₁ sends <Ready T₁> to T_C.

P₂ sends <Ready T₁> to T_C.

P₂ crashed after sending <Ready T₁> to T_C.

P₂ recovered immediately after crash.

a) T_C sends <Commit T₁> to P₁ and P₂

b) T_C sends <Abort T₁> to P₁ and P₂.

c) T_C sends <Commit T₁> only to participant P₁.

d) T_C sends <Abort T₁> only to participant P₂.

Answer: (a) TC sends <Commit T1> to P1 and P2 It is given that the transaction coordinator sent a prepare message to all the participating sites and in-turn all the participants responded with ready message. After that P2 crashed and recovered. We can understand that the crash and recovery happened before the coordinator responds. Whether the participating sites crashed or not, the coordinator will respond based on the messages it received from the participating sites. Hence, in this case, Tc will send the commit message to all the participants.

 

3. After the event “T_C sends <Prepare T₁> to P₁ and P₂”, P₁ decides to commit transaction T₁. Which of the following is true about P₁ with respect to 2PC protocol?

a) P₁ sends <Ready T₁> to T_C and then writes <Ready T₁> into its local log

b) P₁ writes <Ready T₁> into its local log and then sends <Ready T₁> to T_C

c) P₁ sends <Ready T₁> to T_C and then writes <Commit T₁> into its local log

d) P₁ writes <Commit T₁> into its local log and then sends <Ready T₁> to T_C

Answer: (b) P1 writes <Ready T1> into its local log and then sends <Ready T1> to TC In 2PC, if a participating site decided to commit or abort, it has to first register the decision into local log file, flush the log file into disk and then reply with the appropriate message to the coordinator site.

 

4. Which of the following will happen if P₂ is not ready to commit T₁ after the following events?

T_C sends <Prepare T₁> to P₁ and P₂.

P₁ sends <Ready T₁> to T_C.

a) P₂ sends <Commit T₁> to T_c.

b) P₂ writes <Abort T₁> to its local log and sends <Abort T₁> to T_c.

c) P₂ writes <Abort T₁> to its local log and sends <Abort T₁> to T_c and P₁.

d) P₂ writes <No T₁> to its local log and sends <Abort T₁> to T_C.

Answer: (d) P2 writes <No T1> to its local log and sends <Abort T1> to TC According to 2PC, if a participating site has decided not to commit, it has to write <No T> message into its log and send <Abort T> to the transaction coordinators.

 

5. Which of the following will happen after the following sequence of events is completed as per Two Phase Commit (2PC) protocol?

T_C sends <Prepare T₁> to P₁ and P₂.

P₁ sends <Ready T₁> to T_C.

P₂ sends <Abort T₁> to T_C.

a) T_C sends <Commit T₁> to P₁ and P₂

b) T_C sends <Abort T₁> to P₁ and P₂.

c) T_C sends <Commit T₁>, only to participant P₁.

d) T_C sends <Abort T₁>, only to participant P₂.

Answer: (b) TC sends <Abort T1> to P1 and P2 It is given that the transaction coordinator sent a prepare message to all the participating sites. One of the sites is not ready to commit the transaction. In this case, the coordinator has to abort the transaction and inform all the participating sites to abort T1.

 

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Multiple Choice Questions with Answers in Distributed Database

 

1. In distributed query processing, which of the following layer activities are performed by central control site?

a) Query decomposition

b) Data localization

c) Global optimization

d) Distributed execution

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Ans : (a), (b), and (c)

Answer: (a), (b), and (c) Query decomposition, data localization, global optimization, and distributed execution are the four layers of distributed query processing. The first three layer activities are performed at the central control site using the schema information stored in the global directory. The fourth layer performs distributed query execution by executing the plan and returns the answer to the query. This is performed at local sites.

 

2. Which of the following is NOT a step of query decomposition layer in distributed query processing?

a) Normalized query is analyzed semantically

b) Semantically correct query is simplified

c) Simplified calculus query is restructured as an algebraic query

d) The algebraic query is executed by the local sites

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Ans : (d)

Answer: (d) The algebraic query is executed by the local sites Query decomposition layer converts the calculus query into an algebraic query on global relations. This can be performed through four successive steps; The calculus query is rewritten in a normalized form Normalized query is analyzed semantically Semantically correct query is simplified Simplified calculus query is restructured as an algebraic query

 

3. Which of the following is/are NOT locking protocols used in distributed DBMS environment?

a) Centralized 2PL

b) Primary copy 2PL

c) Rigorous 2PL

d) Majority locking based 2PL

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Ans : (c)

Answer: (c) Rigorous 2PL Rigorous 2PL is a two phase locking protocol used in DBMS environment to ensure serializability. Centralized 2PL – a single site acts as the lock manager site and maintains all locking information. Primary copy 2PL – Unlike single site for all data items in centralized 2PL, primary copy 2PL chooses primary copy for each replicated data item. Each such primary copy is maintained in a site and that site acts as the lock manager for that particular data item alone. This way, lock managers are distributed here. Majority locking - When a transaction wishes to read or write a data item that is replicated at n sites, it must send a lock request to more than half of the n sites where the item is stored. The transaction cannot proceed until it obtains locks on a majority of the copies.

 

4. Let us assume that in 2PC protocol a transaction coordinator failed after a decision is taken (to abort/commit) and shared among the participating sites. What should the coordinator do during restart (recovery)?

a) Abort the transaction in any case

b) Commit the transaction in any case

c) Commit/abort only if received all acknowledgements from participating sites

d) Cannot be decided by the coordinator on what to be done

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Ans : (c)

Answer: (c) Commit/abort only if received all acknowledgements from participating sites During recovery, the transaction coordinator in 2PC can perform either commit or abort a transaction based on the decision taken and shared with the participating sites before failure. Commit or abort can be performed only if the coordinator received all the acknowledgements from the participating sites on the decision taken by it.

 

5. Which of the following is NOT an advantage of data replication in distributed database?

a) Fast access to shared data

b) High availability

c) Reduced network traffic

d) Easy updating of data items

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Ans : (d)

Answer: (d) Easy updating of data items Data replication is one of the strategies used in distributed database to distribute the database and its manipulation. As per this strategy, the data is replicated in several sites so as to improve the availability. As we have same data as several different locations, it is hard to update them. Also, during update those data items will not be available to other transactions in order to maintain consistency.

 

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Multiple Choice Questions with Answers in Distributed Database

1. Which of the following would improve the availability of resources especially for reading in a distributed database system?

a) Fragmentation of database

b) Replication of database

c) Defragmentation of database

d) Tuning of database

View Answer

Answer: (b) Replication of database Replication in distributed database system is a concept of having multiple copies of same data at different sites to increase the availability of resources.

2. ______________ is very much required to process a query in a distributed database.

a) Global System Catalog

b) Database Views

c) Triggers

d) None of the above

View Answer

Answer: (a) Global System Catalog Data dictionary is an important component in DBMS. It is used for manipulating information regarding all database components in a DBMS. It stores information regarding tables, views, name of the tables, attributes, constraint details etc. Global System Catalog is just like Data Dictionary for Distributed Database System. It stores information like what and where about the data in a DDB.

3. Reliability and availability of a “Centralized Data Allocation” method is ___________ when compared to a “Completely Replicated Data Allocation“.

a) Highest

b) Average

c) Lowest

d) Not applicable

View Answer

Answer: (c) Lowest Replication in distributed database system is a concept of having multiple copies of same data at different sites to increase the availability of resources. In a centralized data allocation method only one copy of data available. Hence, availability is lowest. Due to only one copy of data, it is prone to single point of failure. In a completely replicated data allocation method, due to availability of more than one copy of same data, the reliability and availability is high compare to centralized data allocation method.

4. If one site ABORTs while processing part of a distributed transaction t, all other sites processing part of t will also ABORT t. Which of the following ensures this?

a) Two phase locking protocol

b) Two phase commit protocol

c) Three phase commit protocol

d) All of the above

View Answer

Answer: (b) Two phase commit protocol In two phase commit protocol, the transaction coordinator decides to ABORT the entire transaction if any of the participating sites cannot commit for some reasons.

5. Which of the following transparencies in distributed database design requires the end user or programmer to specify the database fragment names but need not specify where these fragments are located?

a) Transaction

b) Location

c) Local mapping

d) Fragmentation

View Answer

Answer: (b) Location Location transparency refers to the fact that the command used to perform a task is independent of both the location of the data and the system on which an operation is carried out.

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• Go to Distributed Database Quiz page

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Distributed database multiple choice questions with answers

important quiz questions in DDB

one mark questions in distributed database for university examinations