Dump space allocation in a coupling facility

Dump space is storage you define using the DUMPSPACE parameter in the coupling facility resource management (CFRM) policy. It is set aside for the creation of dump tables. Dump tables are portions or snapshots of a structure typically saved for application development or problem determination purposes. The coupling facility allocates dump space in multiples of the coupling facility storage increment.

Dump tables for several different structures can exist in dump space at the same time. The amount of storage in any one dump table depends on the following factors:

• Amount of information you want to save to a dump table

  The software subsystem can request the portions of a structure that are to be captured in the dump table. For example, lock tables, lists within a list structure, or directory entries belonging to particular storage classes or castout classes.

• Free dump space

  Structures share dump space. If a structure is using some of the dump space, other structures cannot use that portion of the dump space until it is released.

• Characteristics of the structure saved to a dump table

  When saving structure objects to a dump table, the amount of dump space used depends on the parameters specified for the structure. For example, list entry size, the number of list entries in a specified list, the number of directory entries in a castout class, or whether adjunct data is included.

The coupling facility can return the maximum requested dump space value. This value indicates the largest amount of dump space requested by the software subsystems using the coupling facility. This value allows you to adjust the amount of allocated dump space to better match actual usage.