If the session performs incremental aggregation, the PowerCenter Integration Service process saves index and data cache information to disk when the session finished. The next time the session runs, the PowerCenter Integration Service process uses this historical information to perform the incremental aggregation. By default, the DTM creates the index and data files in the directory configured for the $PMCacheDir service process variable. The PowerCenter Integration Service process names the index file PMAGG*.dat and the data file PMAGG*.idx.