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DBMS Estimating Query Cost MCQs

DBMS Estimating Query Cost MCQs: This section contains multiple-choice questions and answers on Estimating Query Cost in DBMS.
Submitted by Anushree Goswami, on May 07, 2022

1. Calculating the net estimated cost of any plan requires determining the cost of each operation included in the plan and combining the estimated costs to obtain the net estimated cost.

1. Revenue Costs
2. Eligible Costs
3. Estimated Costs
4. None

Answer: C) Estimated Costs

Explanation:

Calculating the net estimated cost of any plan requires determining the cost of each operation included in the plan and combining the estimated costs to obtain the net estimated cost.

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2. The cost of an evaluation plan for a query is based on several factors, including:

1. Accesses to the disk
2. A CPU's time spent executing a query
3. In distributed and parallel databases, communication costs are high.
4. All of the above

Answer: D) All of the above

Explanation:

The cost of an evaluation plan for a query is based on several factors, including:

1. Accesses to the disk
2. A CPU's time spent executing a query
3. In distributed and parallel databases, communication costs are high.

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3. The number of blocks transferred from the disk, along with the number of disks seeks, are used to estimate the cost of a query evaluation plan.

1. Query Estimation Plan
2. Query Evaluation Plan
3. Query Exemption Plan
4. None

Answer: B) Query Evaluation Plan

Explanation:

The number of blocks transferred from the disk, along with the number of disks seeks, are used to estimate the cost of a query evaluation plan.

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4. To estimate the cost, we generally take the ___ case into account.

1. Best
2. Worst
3. Medium
4. None

Answer: B) Worst

Explanation:

To estimate the cost, we generally take the worst case into account.

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5. To estimate the cost of the query ____, it is possible to determine the response time, i.e., the time it takes to execute the plan.

1. Evaluation Time
2. Query Time
3. Plan Time
4. Response Time

Answer: D) Response Time

Explanation:

To estimate the cost of the query evaluation plan, it is possible to determine the response time, i.e., the time it takes to execute the plan.

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6. Response time depends on the contents of the buffer when the query begins its execution.

1. Response
2. Execution
3. Plan
4. Query

Answer: A) Response

Explanation:

Response time depends on the contents of the buffer when the query begins its execution.

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7. With multiple disks present in a system, a question such as "How are disk accesses distributed between the disks?" affects response time.

1. Single
2. Double
3. Triple
4. Multiple

Answer: D) Multiple

Explanation:

With multiple disks present in a system, a question such as "How are disk accesses distributed between the disks?" affects response time.

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8. The optimizers find that reducing the total resource ____ of the query plan is more important than minimizing response time for queries.

1. Conclusion
2. Consumption
3. Contradiction
4. Conviction

Answer: B) Consumption

Explanation:

The optimizers find that reducing the total resource consumption of the query plan is more important than minimizing response time for queries.

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9. It's a good idea to minimize the resources used to access the disk or use the extra resources when estimating the cost of a query evaluation plan.

1. Maximize
2. Minimize
3. Mediumize
4. None

Answer: B) Minimize

Explanation:

It's a good idea to minimize the resources used to access the disk or use the extra resources when estimating the cost of a query evaluation plan.

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10. As long as you don't have an in-depth understanding of how the data is presented on the ____, it's hard to estimate.

1. Disk
2. Depth
3. Data
4. None

Answer: A) Disk

Explanation:

As long as you don't have an in-depth understanding of how the data is presented on the disk, it's hard to estimate.

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