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AdsWhat does "Job scheduling" mean ?
Scheduling is related to exploitation which manages plannings of data processing treatments. Its principal role is the tender of batchs, or sequence of batchs, with definite hours when the whole of the conditions are filled. These conditions are generally criteria of dates, statutes of predecessors…
1 March 2007
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Qu’est ce que l’ordonnancement ?
To plan a treatment
The planning of a treatment makes it possible to launch an order on a date and one hour given. It thus corresponds to the first condition of scheduling.
= To define the date
The date can be defined various manners according to the ordonnanceurs but the possibility commonly is found:
: to specify days of the week : to indicate specific days in the year : to calculate public holidays according to a calendar : to use rules of calculation (Ex: 3rd Thursday of the month)
= To define the hours
For the hours, one can as well define a particular hour as a frequency in order to carry out cyclic treatments.
To condition launching
The real interest of scheduling is the installation of conditions which will make it possible to control the production.
= Statutes of jobs A condition of dependence on a statute of job VAr of allowing to define a sequence according to the statutes of the predecessors.
# (images/sequence.png) #
This example presents a sequence of 2 jobs depending on a job A. If job A finishes correctly, the job B starts. In the event of problem on A, it is the job C which is subjected. The way in red is a “degraded way”. *
Certain ordonnanceurs allow to carry out a finer connection by using exit the code of the treatment.
= Control of the resources
The ordonnancor must be able to carry out the minimum of checking on the resources of the machine before the tender of the treatment. Minimum to be checked being the disk space.
Advanced Conditionings
These conditionings are not taken into account by all the ordonnanceurs.
= Action operator
When certain actions cannot be automated, one has recourse to a human intervention. The treatment waits until an operator validated launching to start.
= Variable
It can be possible to condition treatment according to variables, that makes it possible to act on starting by modifying a variable.
To centralize the treatments
= Reference frame
The simple fact of defining the treatments, the accounts of tender and the machines used but more especially the bonds between the applications make of the ordonnancor a reference frame of first level.
= Maitrise of the actions
The operator can act on the treatments or the treatment sequence starting from a single point. The following actions are usually met:
: to subject a treatment : killer a treatment in progress : to block/release a launching : to block/release a sequence In parallel of these actions it is possible to modify the parameters of the treatments.
= simplified Diagnosis
The treatments being centralized, the newspapers of the treatments are directly accessible. In the event of incident the whole of information can be recovered and evaluated by the person in load of the diagnosis.
Management of the queues
The job can be subjected directly on the machine or in a queue, this second method making it possible to manage the priorities of launching between treatments subjected per same hour. The concept of resources and completely virtual and can represent:
a connection (ftp, bases data)
a resource of the machine (CPU, memory…)
= Resources available
# (images/file.png) # a queue can be visualized by pipes in which one can paralellement insert a certain number of tokens. In the example opposite, we defined a queue being able to accept 3 tokens simultaneously. 3 jobs A, B and C can be subjected, one has respectively to affect 2, 3 and 1 to them tokens. These jobs could be subjected per same hour since the regulation will be done in the queue.
= Management of the executions
# (images/file2.png) #
At the time of the tender as of the these 3 jobs, the regulation could be as follows:
: the queue has 3 tokens : job A is subjected and carried out, it consumes 2 tokens : The queue has nothing any more but one token : the job B is subjected but remains execution on standby because it requires 3 tokens : the job C is subjected, it requires only one token, it is thus carried out : at the end of the executions, the resources are released and one has 3 tokens again : the job B is then carried out
= Management of the priorities
To control a queue the management of the priorities is used. In the preceding example, one specifies a priority higher than the job B so that it is put in queue in first position.
To that and safety
= State of the treatments
All the information of execution of the treatments are stored, it is thus possible to know for each treatment:
: the hour of launching : execution time : traces : the statute : possibly exit the code
= To that Any modification and any action are journalized, which makes it possible to follow the treatment but as the actions implemented as it is after the so front incident but. = Safety The speakers must have an account giving access to them the tool according to their role. It is thus possible to give accesses privileged to the direct speakers while leaving free the visualization of the treatments for the applicatives teams.
Management of the incidents
Very alarm went up on the console and returned towards a console of supervision.
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