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Abstract

A plurality of queries (jobs) which consist of sets of tasks with precedence constraints between them are optimally scheduled in two stages of scheduling for processing on a parallel processing system. In a first stage of scheduling, multiple optimum schedules are created for each job, one optimum schedule for each possible number of processors which might be used to execute each job, and an estimated job execution time is determined for each of the optimum schedules created for each job, thereby producing a set of estimated job execution times for each job which are a function of the number of processors used for the job execution. Precedence constraints between tasks in each job are respected in creating all of these optimum schedules. Any known optimum scheduling method for parallel processing tasks that have precedence constraints among tasks may be used but a novel preferred method is also disclosed. The second stage of scheduling utilizes the estimated job execution times determined in the first stage of scheduling to create an overall optimum schedule for the jobs. The second stage of scheduling does not involve precedence constraints because the precedence constraints are between tasks within the same job and not between tasks in separate jobs, so jobs may be scheduled without observing any precedence constraints. Any known optimum scheduling method for the parallel processing of jobs that have no precedence constraints may be used, but a novel preferred method is also disclosed.

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First Claim