Changing the configuration parameters of the cache area

The configuration parameters of a cache area can be modified dynamically using the /MODIFY-DAB-CACHING command. This means that it is no longer necessary to release the cache area explicitly using the /STOP-DAB-CACHING command and then recreate it using the /START-DAB-CACHING (specifying new parameters) command .

The following configuration parameters can be modified dynamically:

• Cache size (CACHE-SIZE):
  The size of a cache area can be expanded or reduced. The cache is reduced without affecting cache utilization for the segment of the cache area that remains.

• Cache segment size (CACHE-SEGMENT-SIZE):
  It is only useful to modify this configuration parameter for cache areas where there is no automatic caching (AREA=*FILE ). All of the value specifications permitted with the /START-DAB-CACHING command are then possible. The cache size can only be modified quasidynamically because of the reorganization of the cache that is required as a result, i.e. caching of the data area is stopped, the cache is saved if necessary and an empty cache is added after reorganization of the cache. The configuration of the database to be cached is retained completely.

• Adapting the cached data area (AREA=*ADD-FILE/*REMOVE-FILE/*RESET-FILE/*ADD-PUBSET/*REMOVE-PUBSET):
  

  AREA=*ADD-PUBSET adds a pubset which has not yet been buffered to a cache area using automatic caching.

  AREA=*REMOVE-PUBSET removes a pubset which has so far been buffered from a cache area using automatic caching.

  AREA=*ADD-FILE adds files to a cache area and AREA=*REMOVE-FILE removes files from a cache area. A distinction must be made here between cache areas with and without automatic caching:

  Cache areas without automatic caching:
  Previously unserved files can be added to the data configuration, or previously served files which had a poor hit rate, for example, can be eliminated from the data configuration.
  Cache areas with automatic caching:
  The caching of files can be influenced directly without the monitoring algorithms of automated caching, i.e. files which are added to the data configuration are always cached or files which are removed are no longer cached.

  AREA=*RESET-FILE resets modifications for files, and the files are once more cached automatically.

• Modifying the threshold for buffering (FORCE-OUT):
  The threshold for the start of buffering for the cache can be set to one of three possible values: *NO, *AT-HIGH-FILLING or *AT-LOW-FILLING.

• Modifying the caching mode (CACHING-MODE):
  
  There are two different “directions”:

  • When changing from *READ to *READ-WRITE/*WRITE/*BY-CACHE-MEDIUM, the data imported in read mode is retained and is processed further in the new mode concerned from this point on.

  • In the other direction (to *READ), data is written to the disk(s) without a disk copy; only read data is then imported in the cache.