# Reducer tab

![Reducer tab, Pentaho MapReduce](https://2745965000-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FvZoINBz5C5WnDZQlbOJQ%2Fuploads%2Fgit-blob-238461f0996a2f1fa41ba2e970a9431299bf61e0%2FssPDIMapReduceEntry-ReducerTab.png?alt=media)

The following table describes the options for defining a reducer transformation:

| Option                                        | Definition                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
| --------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| **Transformation**                            | <p>Specify the transformation that will perform the reducer functions for this job by entering its path or clicking <strong>Browse</strong>.</p><p>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 <strong>${Internal.Entry.Current.Directory}</strong> internal variable to define the path.</p><p>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.</p><p><strong>Note:</strong> Transformations previously specified by reference are automatically converted to be specified by name within the Pentaho Repository.</p> |
| **Input step name**                           | Specify the name of the step that receives reducing data from Hadoop. It must be a MapReduce Input step.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
| **Output step name**                          | Specify the name of the step that passes reducing 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 reducer 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.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |