Cache Files
When you run a mapping, the Data Integration Service creates at least one cache file for each Aggregator, Joiner, Lookup, Rank, and Sorter transformation. If the Data Integration Service cannot run a transformation in memory, it writes the overflow data to the cache files.
The following table describes the types of cache files that the Data Integration Service creates for different mapping objects:
Mapping Object | Cache File |
|---|
Aggregator, Joiner, Lookup, and Rank transformations | The Data Integration Service creates the following types of cache files: - - One header file for each index cache and data cache
- - One data file for each index cache and data cache
|
Sorter transformation | The Data Integration Service creates one sorter cache file. |
When you run a mapping, the Data Integration Service writes a message in the mapping log indicating the cache file name and the transformation name. When a mapping completes, the Data Integration Service releases cache memory and usually deletes the cache files. You might find index and data cache files in the cache directory under the following circumstances:
- •You configure the Lookup transformation to use a persistent cache.
- •The mapping does not complete successfully. The next time you run the mapping, the Data Integration Service deletes the existing cache files and creates new ones.
Because writing to cache files can slow mapping performance, configure the cache sizes to run the transformation in memory.
Cache File Directory
For Aggregator, Joiner, Lookup, and Rank transformations, the Data Integration Service creates the cache files in the directory specified in the Cache Directory property. For Sorter transformations, the service creates the cache files in the directory specified in the Work Directory property.
If the Data Integration Service process does not find the directory, it fails the mapping and writes a message to the mapping log indicating that it could not create or open the cache file. The Data Integration Service may create multiple cache files. The number of cache files is limited by the amount of disk space available in the cache directory.