The first time you run an incremental aggregation session, the Integration Service processes the source. At the end of the session, the Integration Service stores the aggregated data in two cache files, the index and data cache files. The Integration Service saves the cache files in the cache file directory. The next time you run the session, the Integration Service aggregates the new rows with the cached aggregated values in the cache files.
When you run a session with an incremental Aggregator transformation, the Integration Service creates a backup of the Aggregator cache files in $PMCacheDir at the beginning of a session run. The Integration Service promotes the backup cache to the initial cache at the beginning of a session recovery run. The Integration Service cannot restore the backup cache file if the session aborts.
When you create multiple partitions in a session that uses incremental aggregation, the Integration Service creates one set of cache files for each partition.