Tuesday, April 14, 2020

MCQ on distributed and parallel database concepts

MCQ on distributed and parallel database concepts, Interview questions with answers in distributed database

Distribute and Parallel Database – Quiz

1. When a participating site S1 decides to commit the transaction T upon receiving the <prepare T> message from the coordinator, it sends _____ message to the coordinator site.
a) <prepare T>
b) <commit T>
c) <ready T>
d) <abort T>
Answer: (c)
According to two phase commit protocol, if a site is ready for committing a transaction which was already initiated by a coordinator with a <prepare T> message, it will write a <ready T> message into its log, store in its stable storage and send the same to the coordinator site.

2. Why in two phase commit protocol does a participating site first write the decision in its log file before communicating it with the coordinator site?

a) to decide the fate of the transaction if a failure happens
b) to send the all the decisions at once to the coordinator site to reduce the cost.
c) both (a) and (b)
d) neither (a) nor (b)
Answer: (a)
The participant must be able to tell the difference between a crash/failure that occurred before it voted ‘ready’ to Commit from a failure that occurred after it voted ‘ready’ to commit. If on recovery, the participant finds ‘Prepared’ in its log, it knows it voted in favour of committing the transaction, but it does not know the final decision. So it must inquire the Coordinator. If the decision from the Coordinator is to abort, then the participant aborts and rolls-back its sub-transaction.

3. In two-phase commit (2PC) protocol, who can cause a transaction to abort?

a) Coordinator
b) Participating site
c) Both coordinator and participating site
d) Third party site
Answer: (c)

In 2PC, both the coordinator site and the participating site can cause a transaction to abort.

How participating site can do? - If a participating site is not ready to commit a transaction T, then it writes <abort T> in its log file and communicate the same to the coordinator site.
How a coordinator site can do? – If any of the participating sites is not ready to commit, then coordinator decides not to commit and intimate the same to other participating sites.

4. To increase the throughput and response time of the system especially when there are lots of smaller queries, which type of parallelism is most likely to perform better?

a) Intra-query parallelism
b) Inter-query parallelism
c) Inter-operation parallelism
d) Intra-operation parallelism
Answer: (b)
Small queries do not consume much time of the CPU. Inter-query parallelism is a form of parallelism where many different Queries or Transactions are executed in parallel with one another on many processors. It also increases the number of transactions executed in a given time.

5. Which of the following helps in implementing inter-operation parallelism?

a) Interdependent parallelism
b) Intra-query parallelism
c) Inter-query parallelism
d) Pipelined parallelism
Answer: (d)

Inter-operation parallelism is the concept of executing multiple operations of same query in parallel.

The idea behind the pipelined parallelism is to consume the result produced by one operation by the next operation in the pipeline.


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  1. sir,can post a page on equivalence transformation too.

    1. Hi, did you mean equivalence rules for query processing?

    2. yes sir,equivalence rules for query processing


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