PDP Chapter 4: Parallel & Distributed Processing Quiz

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Questions and Answers

What does the critical path length represent in a task dependency graph?

The average processing time of all tasks.

The number of tasks that can be executed simultaneously.

The maximum number of processors needed at any point.

The length of the longest path in the graph. (correct)

Which statement correctly describes the degree of concurrency?

It indicates the maximum number of tasks that can be executed in parallel. (correct)

It is the minimum number of processors required during execution.

It only considers tasks with varying processing times.

It remains constant regardless of task decomposition.

How is the average degree of concurrency calculated?

By taking the sum of all task lengths in the graph.

By measuring the efficiency of processor usage over time. (correct)

By counting the total number of tasks regardless of execution time.

By determining the maximum number of tasks at any point.

What effect does finer granularity in decomposition have on the degree of concurrency?

It increases the degree of concurrency. Signup and view all the answers

In the context of task interaction graphs, which factor may change during program execution?

The degree of concurrency. Signup and view all the answers

What does maximum degree of concurrency indicate?

The peak number of tasks that can execute simultaneously. Signup and view all the answers

What can lead to an increase in the average degree of concurrency?

Increasing parallel task execution efficiency. Signup and view all the answers

Which factor is negatively correlated with the degree of concurrency?

The granularity of task decomposition. Signup and view all the answers

What is the purpose of decomposition in parallel programming?

To create independent, programmable tasks for concurrent execution Signup and view all the answers

Which of the following statements is true regarding task dependency graphs?

They illustrate tasks that require the result of previous tasks for execution. Signup and view all the answers

How does the degree of concurrency impact the performance of parallel processing?

Increased concurrency allows more tasks to be executed simultaneously, potentially reducing overall execution time. Signup and view all the answers

What distinguishes recursive decomposition from other decomposition techniques?

It allows for repeated division of tasks until the smallest manageable units are formed. Signup and view all the answers

Which of the following best describes task interaction in parallel processing?

Tasks frequently require shared data, leading to potential performance bottlenecks. Signup and view all the answers

What is the critical path length for the first task dependency graph?

27 time units Signup and view all the answers

What is the shortest parallel execution time for the second decomposition?

34 time units Signup and view all the answers

What is the serial time (Ts) for the graph with a critical path length of 27?

63 time units Signup and view all the answers

Which formula is used to calculate efficiency in relation to parallel execution?

E = Ts / (p * Tp) Signup and view all the answers

How many processors are required to achieve the minimum parallel execution time for the first decomposition?

4 processors Signup and view all the answers

What is the maximum degree of concurrency possible in the task dependency graphs?

4 Signup and view all the answers

If each search task takes 1 time unit, how long is the average degree of concurrency?

2.33 Signup and view all the answers

What misconception might arise regarding the relationship between serial time and parallel execution time?

Serial time is always less than or equal to parallel execution time. Signup and view all the answers

How can recursive decomposition impact task performance in parallel processing?

It can increase task independence. Signup and view all the answers

In a parallel processing scenario, what factor could influence the overall efficiency significantly?

Task dependency and scheduling Signup and view all the answers

What is the primary purpose of decomposing a query into tasks?

To make the execution of the query more efficient Signup and view all the answers

What does an edge in a task dependency graph represent?

The need for output of one task to complete another Signup and view all the answers

Which factor primarily limits parallel performance in query processing?

Task dependencies and communication overhead Signup and view all the answers

What is a key benefit of recursive decomposition in query processing?

It helps reduce redundancy in task execution Signup and view all the answers

What does the degree of concurrency in task execution refer to?

The number of tasks that can operate simultaneously Signup and view all the answers

Which technique is employed to manage and optimize task interactions during query processing?

Task interaction graphs Signup and view all the answers

How does task interaction in a query processing environment affect performance?

It can lead to increased communication delays and reduced overall efficiency. Signup and view all the answers

Which scenario illustrates a limits on parallel performance?

Tasks are highly dependent on each other. Signup and view all the answers

What key factor does recursive decomposition rely on?

The ability to break tasks into simpler subtasks Signup and view all the answers

Which of the following is essential for recognizing task interactions?

The task interaction graph Signup and view all the answers

What does the critical path length in a task dependency graph indicate?

The longest sequence of dependent tasks. Signup and view all the answers

Which of the following would most likely improve parallel performance during query processing?

Decomposing tasks into smaller subtasks. Signup and view all the answers

What effect does task interaction have on parallel performance?

It can lead to increased bottlenecks if tasks depend on one another. Signup and view all the answers

In recursive decomposition, a task is divided into what type of structure?

A series of nested tasks. Signup and view all the answers

Which decomposition technique involves analyzing task dependencies closely?

Hierarchical decomposition. Signup and view all the answers

What is likely to happen if a task has a high degree of concurrency?

Parallel execution becomes more efficient. Signup and view all the answers

Which of the following statements best describes task decomposition in database query processing?

Breaking down a query into smaller tasks can lead to better resource utilization. Signup and view all the answers

What is a significant characteristic of task dependency graphs?

They indicate the execution order based on dependencies. Signup and view all the answers

Why is task decomposition important for query processing?

It allows tasks to be processed in parallel more effectively. Signup and view all the answers

How does changing the decomposition of a task impact performance?

It can lead to varied parallel execution times. Signup and view all the answers

Study Notes

Critical Path Length

Critical path length refers to the longest path in a task dependency graph, dictating the minimum execution time in parallel processing.
It is essential for determining resource allocation and task scheduling in parallel computing.

Degree of Concurrency

Degree of concurrency signifies the number of tasks that can run in parallel.
Maximum degree reflects the highest count of concurrent tasks at any execution point, indicating the required number of processors.
Average degree of concurrency is assessed to evaluate processor utilization efficiency.
Finer granularity in task decomposition enhances the degree of concurrency.

Case Study: Database Query Processing

Critical path lengths are determined for task dependency graphs with two query decompositions, resulting in lengths of 27 and 34 time units.
Shortest parallel execution times for each decomposition denote optimal processing efficiency.
Serial time (Ts) reflects the total execution time of all tasks executed sequentially, measured as 63 and 64 time units for respective cases.
Efficiency (E) metric calculates how effectively parallel processing capitalizes on total execution time using the formula E = Ts / (p.Tp), yielding efficiencies of 58.25% and 47%.

Query Decompositions

Execution of database queries can be organized into multiple subtasks, generating intermediate results for each clause.
Outputs from one task often serve as inputs for subsequent tasks, forming a directed task dependency graph.
Different decompositions can significantly affect overall performance, emphasizing the importance of strategic planning in parallel task execution.

Dependency Graphs and Decomposition

Decomposition involves partitioning tasks into smaller units designed for potential parallel execution.
A task dependency graph visually represents tasks (nodes) and the necessary order of execution (edges), crucial for planning parallel algorithms.
Independent tasks can be executed simultaneously, such as computing elements in a matrix-vector multiplication, which enhances overall efficiency.

Overall Methodology in Parallel Processing

Initial parallel algorithm development requires task decomposition based on dependencies in the computation.
Each decomposed task's performance and its relationship to others must be evaluated to optimize execution time and resource usage in parallel processing environments.

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Description

Test your knowledge on critical path length and degree of concurrency in task dependency graphs. This quiz covers key concepts from the field of parallel and distributed processing, helping you understand how tasks can be executed simultaneously.