The cache hit rate, i.e. the ratio of read and write hits to the total number of accesses, is decisive for system performance. Apart from the available cache size, the hit rate is dependent on the probability of the data last accessed or adjacent data being processed again, i.e. on the spatio-temporal locality of accesses. The cache hit rate depends not only on the selection of the data (files) to be cached, but also on the setting selected for the cache parameters.
DAB offers the following two options for deciding on which applications are to be expedited by DAB and which files or volumes should profit from DAB caching:
Automatic caching (AutoDAB)
Here DAB selects the files to be cached itself on the basis of its observation of the data flow and cache hit behavior, and adjusts the settings dynamically. This ensures that only files with a good cache hit rate are buffered.Manual caching
Here users select the files to be cached themselves on the basis of their detailed knowledge of applications and their data access behavior, and also choose corresponding cache parameters. They must handle dynamic adjustments themselves.