Distributed database quiz questions with answers, MCQ in distributed database, solved exam questions in distributed and parallel database, distributed query processing, data replication
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)
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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.
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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)
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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
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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)
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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.
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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)
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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.
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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)
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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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