How to split and sync a dynamic number of job instances in a job chain

Scope

• Use Case
  • Run a specific job within a job chain in multiple parallel instances, i.e. split a job for parallel processing.
    • The use case is intended for execution of the same job within a job chain in parallel instances, not for parallel execution of different jobs.
    • Typically each job instance is focused, e.g. on a partition in an Oracle database. The job chain is intended to query database partitions in parallel and to be parameterized individually.
  • Synchronize jobs after parallel processing.
• Solution Outline
  • The number of parallel job instances is dynamically determined by an initial job.
  • Subsequently the respective number of orders is created for a specific job that would be executed in parallel tasks. The number of parallel tasks can be restricted by a process class, forcing job instances to wait for a task to become free.
  • Finally the parallel job instances are synchronized for further processing.
• References
  • How to split and sync jobs in a job chain

Solution

• Download parallel_job_instances.zip
• Extract the archive to a folder ./config/live/issues of your JobScheduler installation.
• The archive will extract the files to a folder parallel_job_instances. 
• You can store the sample files to a any folder as you like, the solution does not make use of specific folder names or job names.

Pattern

Implementation

Components

• The job chain provided by the sample is not specifiic for this solution, the same applies to the query job..
• The prepare job is used to dynamically calculate the number of parallel instances of the query job. This job creates an order parameter parallel_executions=5 for use with the subsequent generate job.
• The generate job implements the solution by creating the number of orders specified by the parallel_executions parameter. 
  • Each order is added the following parameters
    
    • number_of_orders: a copy of the parallel_executions parameter.
    • order_sequence: the sequence number of the order created. The sequence starts from 1 up to the value of the parallel_executions parameter.
    • synchronize_required_orders: the number of orders that the synchronize job waits for. This includes the value of the parallel_executions parameter incremented by 1 for the main order. The prefix synchronize of the parameter name reflects the state that the synchronize job node is assigned in the job chain.
  • The orders are assigned the state that is associated with the next job node, the query job, i.e. the orders will be executed starting with that state.
  • The orders are assigned the end state that is associated with the synchronize job.
• The query job is configured for a maximum number of 3 parallel tasks via the attribute <job tasks="3">. It could be configured for any number of parallel tasks. For the sake of this sample the limitation shows the behavior of the job to wait for processes to become free that could be assigned to subsequent orders for the same job.
• The job synchronize is used to synchronize splitted orders and is provided by the Sync JITL Job with the Java class com.sos.jitl.sync.JobSchedulerSynchronizeJobChainsJSAdapterClass.
  • This job is used without parameters.
• Hint: to re-use the generate job you can
  • store the job to some central folder and reference the job in individual job chains.
  • move the JavaScript code of the job to come central location and use a corresponding <include> element for individual job scripts.

<?xml version="1.0" encoding="ISO-8859-1"?>

<job  order="yes" stop_on_error="no" title="Generate orders for parallel processing" name="generate">
    <params >
        <param  name="sync_state_name" value="synchronize"/>
    </params>
    <script  language="java:javascript">
        <![CDATA[
function spooler_process(){
  
  var currentJobChain = spooler_task.order.job_chain;
  var currentJobChainName = spooler_task.order.job_chain.name;
  params = spooler.create_variable_set();
  params.merge( spooler_task.params );
  params.merge( spooler_task.order.params );
  var numOfOrders = params.value("parallel_executions");
  spooler_log.info(" creating " + numOfOrders + " orders");
  
  var syncParameterName = currentJobChainName + "_required_orders";
  var numOfRequiredOrders = parseInt( numOfOrders )+1;
  params.set_var( syncParameterName, numOfRequiredOrders );
   
  for (var i = 1; i <= numOfOrders; i++) { 
    var subOrder = spooler.create_order()
    var subParams = spooler.create_variable_set();
    subParams.set_var( "number_of_orders", numOfOrders );
    subParams.set_var( "order_sequence", i );
    subParams.set_var( syncParameterName, numOfRequiredOrders );
    subOrder.params = subParams;
    subOrder.state = spooler_task.order.job_chain_node.next_state;
    subOrder.end_state = params.value( "sync_state_name" );
    currentJobChain.add_order( subOrder );
    spooler_log.info( "order has been added: " + i );
  }
  spooler_task.order.params.set_var( syncParameterName, numOfRequiredOrders );
  spooler_task.order.state = params.value( "sync_state_name" );
  return true;
}
        ]]>
    </script>
    <run_time />
</job>  

Usage

• Add an order to job chain parallel_execution by use of JOC.
• Consider the processing that would 
  • split the execution into 5 subsequent orders that run for the query job.
  • move the current order to the synchronize job node.
• The splitted orders for the query job will arrive in the synchronize job node and will wait for all orders to be completed. With all splitted orders being completed the processing will continue with the job do_something.