Task clustering has been proven to be an effective method to reduce execution overhead and increase the computational granularity of workflow tasks executing on distributed resources. However, a job composed of multiple tasks may have a greater risk of suffering from failures than a job composed of a single task. Our theoretic analysis and simulation results demonstrate that failures can have a significant impact on the runtime performance of workflows that use existing clustering policies that ignore failures. We therefore propose two general failure modeling frameworks (task failure model and job failure model) to address these performance issues. We show the necessity to consider the fault tolerance in the task failure model. Based on the task failure model, we propose three methods to improve the workflow performance in dynamic environments. A simulation-based evaluation is performed and it shows that our approach can improve the workflow makespan significantly for two important applications.
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