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Example: Multiple parallel processes in a job chain
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Specification:
- Write a The job chain that starts with the is to start with a job named "truncate_export_table".
- After this job has been completed four jobs named "table partition" are to be run in parallel.
- A single job that indexes the new partition tables is then to run.
- Finally, a further four jobs that test the individual partition tables are to start in parallel.
This job chain is shown schematically in the diagram in the "Diamond" section below.
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The following steps have to be followed to achieve realize a job chain that meets the requirements listed above:
- A "splitter" job has to be included for each "setseries" of job nodes that are to be processed in parallel. The splitter generates an order for each series of parallel job nodes starts the parallel jobs these orders as soon as it itself is has been started.
- In order to do this the splitter job has to "know" the names of the parallel nodes, which the states corresponding to the first node of each job node series. These names are specified in the splitter job's state_names parameter (see Setting_parameters).
- The parallel processing normally ends at a specific node in the the chain : thereafter with processing continues then continuing serially. This node is the synchronisation node and is implemented using the Sync-Job.
The "Diamond"
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job chain structure
The example job chain will look like this (the diagram has been generated with the Sandbox JOE Version):
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We refer to the pattern that results with this type of job chain as a "diamond" pattern. These diamonds Such patterns can occur more than once in a job chain: both sequentially, as shown in the diagram above, in parallel and nested. They can also be combined with other job chain patterns such as emerald or cross-over patterns (see SynchronizatonSynchronisation_of_Job_Chains).
Job chain list view
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A generic splitter job is delivered with the JobScheduler JITL jobs. This job can be found in the "./live/sos/jitl" directory.
We recommend that you use the following syntax is used for the names of job nodes that are to be processed in parallel:
- "splitter job node name" ":" "job name". In the example diagram above, one of the first nodes would then have the name split_partitions:partition_1.
This syntax Although this syntax is not necessary for the correct functioning of the JobScheduler, it allows the diagram algorithm in JOE (that was used to draw the "diamond" diagram shown above) to know and correctly display the nodes that directly follow on from the splitter. It is necessary to use this type of job name syntax as the syntax used by JobScheduler does not recognize predecessor relationships (only successors).
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Splitter job parameters
See documentation of the JobChainSplitter job JobChainSplitter.
The state_names parameter
- The splitter job state_names parameter is used to specify the node names of the jobs that are to be first started in parallel (see Setting_parameters).
- The node names are to be seperated by semi-colons.
- In jobs chains with this diamond pattern structure, the parameters are specified for the job chain and referred to as node parameters. Node parameters can be used to specify parameters for more than one splitter in a job chain, independently of one another, as in our example, without creating conflicts.
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A unique sync job is required at the end of every set group of processes running in parallel (see Setting_up_a_sync_job) , when further the nodes in the job chain after the sync node are only to be processed after all the jobs (tasks) that are to be carried out in parallel have been completed without errors.
Each sync job has to be unique within a JobScheduler instance - and within a job chain - as long as a cross-over pattern has not been implemented (see Synchronizaton_of_Job_Chains).
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