IBM InfoSphere Streams Version 4.1.1

Setting the degree of parallelism

You can specify the number of channels for user-defined parallelism within the application or as a submission time value.

About this task

The degree of parallelism, also known as the parallel width, is the number of channels in a parallel region.

You can set the degree of parallelism within Streams Studio. For example, in the SPL Graphical Editor, double-click the operator to open the edit view. Within that view, select the annotations tab and edit the parallel field. In the SPL editor, type @parallel and press Ctrl+space for assistance to complete the annotation.

Procedure

You can use any of the following methods to set the degree of parallelism:

Specify a constant value in the width parameter in the @parallel annotation. For example, the following example specifies to replicate the operator 5 times:
```
@parallel(width=5)
  stream<Type> Output = Op(Input) {
    // ...     }
```
Specify a composite operator parameter in the @parallel annotation. For example:
```
composite Sample1(input In; output Out) {
  param expression<int32> $parWidth;      
  graph               
    @parallel(width=$parWidth)
      stream<Type> Out = Op(In) {
      // ...          
      }       
}
```
When you call the Sample1 composite operator in an application, you must supply a value for the parWidth parameter. Alternatively, you can provide a submission-time value for the parameter.

Specify to use a submission-time value in the width parameter in the @parallel annotation. For example:

@parallel(width=(int32)getSubmissionTimeValue("parWidth"))
  stream<Type> Output = Op(Input1, Input2) {
      // ...          
      }       
}

What to do next

If you chose to specify the degree of user-defined parallelism at submission time, you must specify the parameter value when you submit the job. For example:

streamtool submitjob -P parWidth=6 Sample.sab