For each volume set, systems support must define whether a cache is to be used, the cache medium required and the size of the cache area (command MODIFY-PUBSET-CACHE-ATTRIBUTES ...,CACHE-MEDIUM=...,CACHE-SIZE=...).
Specific cache operating parameters must also be specified if a cache is to be used, e.g. MODIFY-PUBSET-CACHE-ATTRIBUTES ...,CACHE-MEDIUM=*MAIN-MEMORY (CACHE-SEGMENT-SIZE =*4KB,FORCE-OUT=*AT-HIGH-FILLING). The extent and meaning of the operating parameters differ for the separate cache media. Systems support defines the values for the cache configurations of the volume sets. They are recorded for each volume set in the SM pubset configuration file (see "Pubset configuration file" in section "Pubset metadata").
In contrast to SF pubsets, the defined values may only be changed during pubset operation.
The values for the volume set cache configuration come into effect:
- If the pubset is operational (IMPORT-PUBSET)
If a volume set was previously in the “defined only” state and a physical volume set configuration was assigned to it via dynamic pubset reconfiguration (with the command MODIFY-PUBSET-PROCESSING ...,VOLUME-SET-SUPPORT= *ADD(...))
If the cache is activated with the START-PUBSET-CACHING command
The system thereby attempts to set up a cache area for the volume set in accordance with the defined values. Size deviations may occur in certain situations. The size of the assigned cache area and the effective cache operating parameters are described by the current values of the volume set cache configuration.
A volume set’s cache area is disconnected:
If the pubset is taken out of operation (EXPORT-PUBSET)
If dynamic pubset reconfiguration is used to revoke the physical volume configuration for a volume set (command MODIFY-PUBSET-PROCESSING ...,VOLUME-SET-SUPPORT=*REMOVE(...))
If the cache is deactivated with the STOP-PUBSET-CACHING command
Pubsets which are not operational are normally not connected to cache areas. Exported SF pubsets or the volume sets of exported SM pubsets may still be assigned cache areas in special cases, e.g. after a system crash.
It is also possible to create cache areas in main memory for shared imported pubsets. These do not take the form of a global cache area for all pubset sharers, but are instead system-local cache areas. Configuration by means of MODIFY-PUBSET-CACHE-ATTRIBUTES (EDIT-PUBSET-CACHE-ATTRIBUTES) is system-local in the case of SF pubsets while the settings apply to all pubset sharers in the case of the volume sets of SM pubsets. For a detailed description of the possible applications, refer to the manual “DAB” [10].