Note pad names and structure selection

The structure names for coupling facility structures to be used for XCF note pads can be of the following forms:
  • IXCNP_SYSXCFxx, and
  • IXCNP_ownerxx
where xx is the EBCDIC representation of a hexadecimal number in the range X'00' to X'FF' and owner is derived from the note pad name in the obvious manner.

When called to create a note pad, the XCF Note Pad Services extract the owner section of the note pad name. The Coupling Facility Resource Management (CFRM) policy is queried to determine whether the installation has defined any structures with names of the form IXCNP_ownerxx. If so, the note pad will be allocated in one of those structures. The term owner specific structures is used to refer to the set of structures with names of this form. If none of the owner specific structures are suitable, the create note pad request is rejected. When creating a new note pad, the set of owner specific structures does not include any structure that is pending delete.

If owner specific structures are not defined for the note pad in the CFRM policy, the note pad is allocated in one of the structures with names of the form IXCNP_SYSXCFxx. The term community structures is used to refer to the set of structures with names of this form. If no community structures are defined in the CFRM policy, or if none of them are suitable for the note pad, the create note pad request is rejected. When creating a new note pad, the set of community structures does not include any structure that is pending delete.

Thus when choosing a structure to host the note pad, the XCF Note Pad Services exclusively consider owner specific structures if any are defined, and exclusively considers community structures if not. It does not, for example, consider owner specific structures and then move on to community structures if none of the owner specific structures are suitable.

An installation can define owner specific structures, community structures, or some combination of the two. Owner specific structures might be defined for some, none, or all the note pads. Generally owner specific structures are defined only if the installation wants to isolate a particular set of note pads in a particular set of structures. Thus the owner section of the note pad name has a direct bearing on the degree to which the installation can manage note pad placement.

When defining the owner section of the your note pad name, consider the following consequences with respect to placement of note pads within owner specific structures. If the installation defines owner specific structures, all of the note pads with the same owner will be allocated in one of those structures. In the most extreme case, this set of owner specific structures could consist of exactly one structure. Depending on the choice of owner, this group of note pads could be large or small.

  • If you specify just your component code as the owner for all your note pads, the note pads for all of your applications across all your product suites across all versions and release levels will be placed together in the same set of structures. This naming technique allows a potentially large number of note pads to be placed within a small set of structures and tends to optimize utilization of space within the coupling facility. However, there might be concerns about such issues as placing note pads for the production workload in the same structures as note pads for applications that are under test.
  • You might append additional characters to your component code to provide more granularity. For example, you might append characters to create groups of note pads based on product suite, or application, or release level, or perhaps some combination thereof. This technique allows the installation to have finer control of the placement of note pads since the number of note pads in the group is presumably smaller. In the extreme case, the owner might be unique for each note pad in which case the owner specific structure would have but one note pad. However, a single note pad per structure does not provide for a particularly efficient use of coupling facility storage.
  • You might provide a way for the installation to optionally define part of the owner in either of the naming techniques above. Doing so would give the installation the ability to group your note pads in meaningful ways. For example, the installation might then be able to isolate note pads for test versions of the application from the production note pads.

Enabling the installation to optionally specify the entirety of the owner section for your note pad names maximizes the ability of the installation to direct placement of the note pads to specific sets of structures as appropriate for the needs of the business. Some installations might even desire, for example, to bundle the note pads of several vendors under the same owner so that a disparate collection of note pads could be placed together in a specific structure. However, doing so could cause conflicts since the owner was intended to provide the uniqueness needed to guarantee that the note pads of different vendors did not collide. So if you allow the installation to define the entirety of the owner section of your note pad name, you likely ought to allow the installation to define the entire note pad name.