CUSTOMER_CODE
SMUDE
DIVISION_CODE
SMUDE
EVENT_CODE
OCTOBER15
ASSESSMENT_CODE BC0050_OCTOBER15
QUESTION_TYPE
DESCRIPTIVE_QUESTION
QUESTION_ID
4176
QUESTION_TEXT
List the objectives of Query processing.
SCHEME OF
EVALUATION
The main objective of the query processing in a distributed environment
is to form a high level query on a distributed database, which is seen as a
single database by the users, into an efficient execution strategy
expressed in a low level language on local database. (2.5 marks)
An important of query processing is query optimization. Because many
execution strategies are correct transformations of the same high level
query, the one that optimizes resource consumption should be retained.
(2.5 marks)
The good measures of resource consumptions are:
The total cost that will be incurred in processing the query. It is incurred
in processing the operations of the query at various sites and intrinsic
communication.
The resource time of the query. This is the time elapsed for executing the
query. Since operations can be executed in parallel at different sites, the
response time is less than its cost. (2.5 marks)
Obviously the total cost should be minimized.
In a distributed system the total cost to be minimized includes CPU,I?O
and communication costs. These costs can minimize by reducing the
number of I/O operations through fast access methods to the data and
efficient use of main memory. The communication cost is time needed
for exchanging the data between sites participating in the execution of
the query.
In centralized system, only CPU and I/O cost have to be considered. (2.5
marks)
QUESTION_TYPE
DESCRIPTIVE_QUESTION
QUESTION_ID
4177
QUESTION_TEXT
What are the different goals of transaction management? Explain.
SCHEME OF
EVALUATION
The goal of the transaction management in a distributed database is to
control the execution of transactions so that:
1.Transactions have atomicity, durability, serializabilty and isolation
properties.
2.Their cost in terms of main memory, CPU and number of transmitted
control messages and their response time are minimized.
3.The availability of the system is maximized. (3 marks)
CPU and main memory utilization: It s a common aspect in both
centralized and distributed database. In case of concurrent transactions
the CPU and main memory should be properly scheduled and managed
by the operating system. Otherwise it becomes a bottle neck when the
number concurrent transaction is more. (2.5 marks)
Control messages: As the control message does not carry any fruitful
data and only they are used to control the execution of transactions.
There should be very less exchange of such messages between the sites.
The obvious reason is the communication cost will be increased
unnecessarily. (2.5 marks)
Response time should be as small as possible for the better performance
of the system. Definitely it will be very crucial as in distributed system
an additional time is required for communication between different sites.
(2 marks) Total 10 marks
QUESTION_TYPE
DESCRIPTIVE_QUESTION
QUESTION_ID
4178
QUESTION_TEXT
List out the memory components of SGA. Explain
Memory components are
a.Redo log buffer
b.The database buffer cache
c.The shared pool
d.The Java pool
SCHEME OF EVALUATION
e.The large pool
f.The streams pool
(1 mark)
Explanation:
For each type 1.5 marks each
QUESTION_TYPE
DESCRIPTIVE_QUESTION
QUESTION_ID
113961
QUESTION_TEXT
Give the 7 steps to be performed by each node except the commit point
site in the prepare phase of two phase commit mechanism. Also give the
3 steps occurring during forget phase.
SCHEME OF
EVALUATION
Steps in the Prepare Phase: To complete the prepare phase, each node
excluding the commit point site performs the following steps:
1.
The node requests that its descendants, that is, the nodes
subsequently referenced, prepare to commit.
2.
3.
4.
5.
6.
7.
The node checks to see whether the transaction changes data on
itself or its descendants. If there is no change to the data, then the
node skips the remaining steps and returns a read-only response
The node allocates the resources it needs to commit the transaction
if data is changed.
The node saves redo records corresponding to changes made by the
transaction to its online redo log.
The node guarantees that locks held for the transaction are able to
survive a failure.
The node responds to the initiating node with a prepared response
or, if its attempt or the attempt of one of its descendents to prepare
was unsuccessful, with an abort response.
These actions guarantee that the node can subsequently commit or
roll back the transaction on the node. The prepared nodes then wait
until a COMMIT or ABORT request is received from the global
coordinator.
(1 mark each)
Forget Phase: After the participating nodes notify the commit point site that
they have committed, the commit point site can forget about the transaction.
The following steps occur:
1.
After receiving notice from the global coordinator that all nodes
have committed, the commit point site erases status information
about this transaction.
2. The commit point site informs the global coordinator that it has
erased the status information.
3. The global coordinator erases its own information about the
transaction.
(1 mark each)
QUESTION_TYPE
DESCRIPTIVE_QUESTION
QUESTION_ID
113965
QUESTION_TEXT
What are the different Troubleshooting problems in Distributed
Transaction?
SCHEME OF
EVALUATION
a.
b.
c.
d.
e.
Failures that interrupt Two-phase commit
Failures that prevent data access
Transaction time-out
Lock from in-doubt transaction
Manually overriding in-doubt transactions
(2 marks each)
QUESTION_TYPE
DESCRIPTIVE_QUESTION
QUESTION_ID
113967
QUESTION_TEXT
Explain the notions of Transparency and Site autonomy
Transparency:
(5 marks)
a.
Location transparency
SCHEME OF EVALUATION
b.
Replication transparency
Site autonomy
(5 marks)