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Questions and Answers
What does the critical path length represent in a task dependency graph?
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?
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?
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?
What effect does finer granularity in decomposition have on the degree of concurrency?
In the context of task interaction graphs, which factor may change during program execution?
In the context of task interaction graphs, which factor may change during program execution?
What does maximum degree of concurrency indicate?
What does maximum degree of concurrency indicate?
What can lead to an increase in the average degree of concurrency?
What can lead to an increase in the average degree of concurrency?
Which factor is negatively correlated with the degree of concurrency?
Which factor is negatively correlated with the degree of concurrency?
What is the purpose of decomposition in parallel programming?
What is the purpose of decomposition in parallel programming?
Which of the following statements is true regarding task dependency graphs?
Which of the following statements is true regarding task dependency graphs?
How does the degree of concurrency impact the performance of parallel processing?
How does the degree of concurrency impact the performance of parallel processing?
What distinguishes recursive decomposition from other decomposition techniques?
What distinguishes recursive decomposition from other decomposition techniques?
Which of the following best describes task interaction in parallel processing?
Which of the following best describes task interaction in parallel processing?
What is the critical path length for the first task dependency graph?
What is the critical path length for the first task dependency graph?
What is the shortest parallel execution time for the second decomposition?
What is the shortest parallel execution time for the second decomposition?
What is the serial time (Ts) for the graph with a critical path length of 27?
What is the serial time (Ts) for the graph with a critical path length of 27?
Which formula is used to calculate efficiency in relation to parallel execution?
Which formula is used to calculate efficiency in relation to parallel execution?
How many processors are required to achieve the minimum parallel execution time for the first decomposition?
How many processors are required to achieve the minimum parallel execution time for the first decomposition?
What is the maximum degree of concurrency possible in the task dependency graphs?
What is the maximum degree of concurrency possible in the task dependency graphs?
If each search task takes 1 time unit, how long is the average degree of concurrency?
If each search task takes 1 time unit, how long is the average degree of concurrency?
What misconception might arise regarding the relationship between serial time and parallel execution time?
What misconception might arise regarding the relationship between serial time and parallel execution time?
How can recursive decomposition impact task performance in parallel processing?
How can recursive decomposition impact task performance in parallel processing?
In a parallel processing scenario, what factor could influence the overall efficiency significantly?
In a parallel processing scenario, what factor could influence the overall efficiency significantly?
What is the primary purpose of decomposing a query into tasks?
What is the primary purpose of decomposing a query into tasks?
What does an edge in a task dependency graph represent?
What does an edge in a task dependency graph represent?
Which factor primarily limits parallel performance in query processing?
Which factor primarily limits parallel performance in query processing?
What is a key benefit of recursive decomposition in query processing?
What is a key benefit of recursive decomposition in query processing?
What does the degree of concurrency in task execution refer to?
What does the degree of concurrency in task execution refer to?
Which technique is employed to manage and optimize task interactions during query processing?
Which technique is employed to manage and optimize task interactions during query processing?
How does task interaction in a query processing environment affect performance?
How does task interaction in a query processing environment affect performance?
Which scenario illustrates a limits on parallel performance?
Which scenario illustrates a limits on parallel performance?
What key factor does recursive decomposition rely on?
What key factor does recursive decomposition rely on?
Which of the following is essential for recognizing task interactions?
Which of the following is essential for recognizing task interactions?
What does the critical path length in a task dependency graph indicate?
What does the critical path length in a task dependency graph indicate?
Which of the following would most likely improve parallel performance during query processing?
Which of the following would most likely improve parallel performance during query processing?
What effect does task interaction have on parallel performance?
What effect does task interaction have on parallel performance?
In recursive decomposition, a task is divided into what type of structure?
In recursive decomposition, a task is divided into what type of structure?
Which decomposition technique involves analyzing task dependencies closely?
Which decomposition technique involves analyzing task dependencies closely?
What is likely to happen if a task has a high degree of concurrency?
What is likely to happen if a task has a high degree of concurrency?
Which of the following statements best describes task decomposition in database query processing?
Which of the following statements best describes task decomposition in database query processing?
What is a significant characteristic of task dependency graphs?
What is a significant characteristic of task dependency graphs?
Why is task decomposition important for query processing?
Why is task decomposition important for query processing?
How does changing the decomposition of a task impact performance?
How does changing the decomposition of a task impact performance?
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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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