Transformation threads write to the cache directory when the Data Integration Service uses cache partitioning and must store overflow values in cache files.

When multiple threads write to a single directory, the mapping might encounter a bottleneck due to input/output (I/O) contention. An I/O contention can occur when threads write data to the file system at the same time.

When you configure multiple cache directories, the Data Integration Service determines the cache directory for each transformation thread in a round-robin fashion. For example, you configure an Aggregator transformation to use directoryA and directoryB as cache directories. If the Data Integration Service uses four threads to run the Aggregator transformation, the first and third transformation threads store overflow values in cache files in directoryA. The second and fourth transformation threads store overflow values in cache files in directoryB.

If the Data Integration Service does not use cache partitioning for the Aggregator, Joiner, Rank, or Sorter transformation, the service stores overflow values in cache files in the first listed directory.

Configure the cache directories in the

Cache Directory

property for the Aggregator, Joiner, or Rank transformation advanced properties. Configure the cache directories in the

Work Directory

property for the Sorter transformation advanced properties. By default, the

Cache Directory

and

Work Directory

properties are configured to use the system parameter values defined for the Data Integration Service. Use the default CacheDir or TempDir system parameter value if an administrator entered multiple directories separated by semicolons for the

Cache Directory

or

Temporary Directories

property for the Data Integration Service.

You can enter a different value to configure multiple cache directories specific to the transformation. Enter multiple directories separated by semicolons for the property or for the user-defined parameter assigned to the property.