By default, the Integration Service uses a non-persistent cache whenever you enable caching in a Lookup transformation. The Integration Service deletes the cache files at the end of a session. The next time you run the session, the Integration Service builds the memory cache from the database.
A persistent lookup cache is the cached data that is preserved for future use. If you want to save and reuse the cache files, you can configure the transformation to use a persistent cache. Use a persistent cache when you know the lookup table does not change between session runs. The first time the Integration Service runs a session using a persistent lookup cache it saves the cache files to disk instead of deleting them. The next time the Integration Service runs the session, it builds the memory cache from the cache files.
The persistent lookup cache can be shared among many Lookup transformations, and these cached file are treated as objects. Before the Integration Service moves data from these cache files to memory cache it acquires lock on the cache files. When the server locks the file it creates a lock file with the .lck extension. Acquiring a lock on cache files is mandatory since this cache is being shared among many transformations. This guarantees that the data in the cache file is not modified when the server is using the data in memory.
When you run a session, if the persistent cache option is enabled, all data is written to the cache file.
The cache file size depends on following factors:
Amount of data. Please refer to the explanation above to determine when the data is cached into cache files.Make sure that you analyze the cache size after the session is finished.
Integration Service Data Movement mode (either ASCII or UNICODE ).
If Lookup transformation is dynamic then the size of the cache file will continually increase, since data might be added to the cache files (when a record is not found in lookup cache) on each run.
FAQ: Can the same persistent lookup cache be used with multiple PowerCenter mappings? (21533)
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