The Shape writer can index shape data by attribute and produce attribute index files. These files are named as <featureClass>.<attributeName>.atx. FME attempts to index all attributes that are flagged as INDEX in the user attributes tab of the FME Workbench Feature Type Properties.
Any attribute of type char or number that is indexed must be at most 80 characters wide. Additionally, attribute names cannot contain characters that are illegal in Windows filenames.
If any attributes are flagged for indexing, FME automatically produces spatial index files for the feature type, regardless of the Write Spatial Index setting in the FME Workbench writer parameters dialog. For more information, see the writer parameter Write Spatial Index.
Writing attribute indexes requires that FME is running on a machine with ArcGIS installed.