The variance of flow-time and variance of waiting-time performance measures are analyzed for the single machine sequencing problem. These measures are compared and contrasted to the performance measures of mean flow-time and mean waiting-time. In particular, while the two mean performance measures attain their minimums at the same job sequence, it is shown that the sequence that minimizes the variance of flow-time is antithetical to the sequence that minimizes the variance of waiting-time. However, the minimum values of the two variance measures are equal. Relationships are also derived for the special problems where either all the job processing-times are equal or all the job weights are equal.
This paper deala with the sequencing problem of minimizing linear delay costs with parallel identical processore. The theoretical properties of this m-machine problem are explored, and the problem of determining an optimum scheduling procedure is examined. Properties of the optimum schedule are given an well an the corresponding reductions in the number of schedules that must be evaluated in the search for an optimum. An experimental comparison of scheduling ruks is reported; this indicates that although a clam of effective heuristics CM be identified. their relative behavior is difficult to characterize.
A computer systems designer is faced with a decision concerning the organization of data files.He often would like to design a file so that sequential and random processing can both be performed efficiently.Two file organizations often proposed for these processing requirements are indexed sequential and direct. Another technique called "batch random" has been proposed for the batch updating of direct access files.Discrete simulation models of these file organizations and access methods in both transaction and batch processing modes are developed and used to analyze the file organizations.A general guideline is derived to indicate whether batch or transaction processing should be performed based on the percentage of the file which is to be processed.Based on these results, a methodology for selecting the "best" file organization is developed for a given set of criteria.Not all the parameters for describing a file organization are incorporated into the methodology and therefore "best" does not necessarily mean optimal.
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