The most important consideration when using DAB is to decide which applications can be accelerated by DAB and which files or disks are to be cached with DAB. A good knowledge of the overall system I/O load and the I/O access behavior of performance-critical applications is required for optimum selection of the database for DAB use.
To facilitate the above, DAB offers automatic, intelligent selection of the data in addition to manual selection (through explicit specification of the files to be buffered). Automatic DAB mode can be set for each cache area; the base function is called AutoDAB. In the simplest case, the entire available cache memory is configured as a cache area by systems support for all disks that affect performance, and file selection is left to AutoDAB, which ensures that frequently used files are buffered with a good hit rate while files which react unfavorably to caching are not cached.
AutoDAB provides the following functions:
files suitable for caching are selected automatically from a set of volumes by means of intelligent caching algorithms
the prefetch factor is set to match the access profile of the selected files
the cache utilization of the buffered files is monitored cyclically
the AutoDAB functions are described in detail from "Automatic caching (AutoDAB)".
The cache areas are created with the /START-DAB-CACHING AREA=*BY-SYSTEM command.