> For the complete documentation index, see [llms.txt](https://docs.pentaho.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.pentaho.com/pdia-data-integration/10.2-data-integration/pdi-job-entries-reference-overview/pentaho-mapreduce/options-pentaho-mapreduce-job/combiner-tab.md).
# Combiner tab
The following table describes the options for defining a combiner transformation:
| Option | Definition |
| --------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| **Transformation** | Specify the transformation that will perform the combiner functions for this job by entering its path or clicking Browse.
You can use any internal variable to specify the path. For example, if you select a transformation that is located in the same folder as the current transformation, you can use the ${Internal.Entry.Current.Directory} internal variable to define the path.
If you are working with a repository, specify the name of the transformation in your repository. If you are not working with a repository, specify the XML file name of the transformation on your system.
Note: Transformations previously specified by reference are automatically converted to be specified by name within the Pentaho Repository.
|
| **Input step name** | Specify the name of the step that receives combiner data from Hadoop. It must be a MapReduce Input step. |
| **Output step name** | Specify the name of the step that passes combiner output back to Hadoop. It must be a MapReduce Output step. |
| **Use single threaded transformation engine** | Select to indicate the Single Threaded transformation execution engine should be used to execute the combiner transformation. If not selected, the normal multi-threaded transformation engine will be used. The Single Threaded transformation execution engine reduces overhead when processing many small groups of output. |
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