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Scheduling and Job scheduling

The difference between planning and scheduling is the use of the resources necessary. Scheduling thus takes into account the constraints of the projects, that induces the concept of optimization.

= Planning

Planning consists in establishing an organization according to a general plan. Whereas scheduling attempts to lay out and to arrange information. To make a parallel with data processing, one can estimate that the cron or orders it At make it possible to plan. It will be possible to organize launchings of the treatments by indicating the times of departures. One can then obtain a plan listing the treatments and their times of departure. At the hour indicated, the treatment will be launched some is the state of the other treatments and the resources necessary. The stock management is done simply by adding margins between the treatments. These margins can be refined according to the evolutions of the processing times, in case this margins insufficient, the plan is modified to take into account the shift.

= Scheduling

Scheduling takes into account the various constraints of the environment, the time of departure is not thus more one condition sufficient for launching of the treatment. To remove the margins and thus to optimize the processing times, one can bind the batchs between them according to their statutes or of finer elements such as the code of exit. The launching of a treatment is not any more according to one hour given and established by a plan but directly at the end of a preceding treatment. These constraints can also be technical, the conditions will be based on criteria of resources systems which are material (CPU, memory…) or software (presence of process, files…).

= Scheduler

The cron is a scheduler, one makes use of it to plan treatments on Unix. It is however not possible of “séquencer” the treatments, it is thus not a ordonnancor as one can generally read it. To distinguish different “the schedulers”, one uses the terms “job scheduling” to mean that it is about a planning of jobs but especially, and that is only induced, that these jobs are dependent between them. For the ordonnanceurs évènementiels whose mechanism rests on events, one will specify “vent-driven job scheduling rather”.

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