Persistent Lookup Cache
A persistent lookup cache is a cache that the Integration Service reuses for multiple runs of the same mapping. Use a persistent lookup cache when the lookup source does not change between mapping runs.
By default, the Integration Service uses a non-persistent cache when you enable lookup caching in a Lookup transformation. The Integration Service deletes the cache files when the mapping completes. The next time you run the mapping, the Integration Service builds the memory cache from the lookup source.
If you configure the Lookup transformation to use a persistent lookup cache, the Integration Service saves and reuses cache files for multiple runs of the mapping. A persistent cache eliminates the time required to read the lookup table and rebuild the lookup cache.
The first time the Integration Service runs a mapping with a persistent lookup cache, the Integration Service saves the cache files to disk. The next time the Integration Service runs the mapping, it builds the memory cache from the cache files.
You can configure the Integration Service to rebuild a persistent lookup cache if the original lookup source changes. When you rebuild a cache, the Integration Service creates new cache files and writes a message to the Integration Service log.
Rebuilding a Persistent Lookup Cache
You can configure the Integration Service to rebuild the persistent lookup cache. In some cases, the Integration Service will rebuild the persistent lookup cache even if you do not configure it to.
Consider the following rules and guidelines when you rebuild a persistent lookup cache:
- •Rebuild a persistent lookup cache if the lookup source changed since the last time the Integration Service built the cache.
- •You can rebuild the cache when the mapping contains one or more Lookup transformations that share a cache.
- •If the lookup table does not change between mapping runs, configure the Lookup transformation to use a persistent lookup cache. The Integration Service saves and reuses cache files, eliminating the time required to read the lookup table.
- •If you configure subsequent Lookup transformations to rebuild the lookup cache, the Integration Service shares the cache instead of rebuilding the cache when it processes the subsequent Lookup transformation.
- •If a mapping contains two persistent lookups and you configure the second Lookup transformation to rebuild the cache, then the Integration Service rebuilds the persistent lookup cache for both.
The Integration Service rebuilds the persistent lookup cache in the following scenarios:
- •The Integration Service cannot find the cache files.
- •The Integration Service cannot reuse the cache. In this instance, it either rebuilds the lookup cache or fails the mapping.
- •You enable or disable high precision for the Integration Service.
- •You edit the Lookup transformation or the mapping.
Note: The Integration Service does not rebuild the cache if you edit the transformation description.
- •You change the number of partitions.
- •You change the database connection or the file location used to access the lookup source.
- •You change the sort order in Unicode mode.
- •You change the Integration Service code page.