Selecting the Entry-To-Element Ratio

You cannot control directly the number of list entries or data elements the list structure will hold. The installation uses the CFRM policy to specify the amount of storage a particular list structure will occupy. When the list structure is allocated and, if applicable, the percentage of list structure storage has been set aside for event monitor controls objects, the list structure storage is subdivided to reserve space for list structure components such as data elements and list entry controls. The value you specify for the entry-to-element ratio is used by the system to determine the proportion of the list structure storage to allocate to each component. The ratio, expressed as a pair of whole numbers, such as 1:4, is passed to IXLCONN using the following ENTRYRATIO and ELEMENTRATIO parameters.

The ENTRYRATIO parameter specifies the part of the ratio for the list entry controls (for instance, the 1 in the 1:4 ratio)
The ELEMENTRATIO parameter specifies the part of the ratio for the data elements (for instance, the 4 in the 1:4 ratio).

In general, the entry-to-element ratio should reflect the average number of data elements per list entry. For example, if your data element size is 4096 byes, and you estimate that about half of the list entries will require 1 data element and about half of the list entries will require 8 data elements, then you would want a ratio of 1:4.5 which you would express in whole numbers as 2:9.

Although you request a particular entry-to-element through the IXLCONN macro, the system might use a slightly different ratio. The actual number of entries and elements in the structure, rather than the ratio, is returned to you in the IXLCONN answer area mapped by the IXLYCONA macro. Note that these values in IXLYCONA are not exact values because the coupling facility might reserve some entries and elements for its own use. The reserved entries and elements are not available for your use, but are accounted for in the IXLYCONA counts.

If the entry-to-element ratio is incorrect for your use of the list structure, you will encounter frequent rejections of IXLLIST requests because the list structure is full. If you are monitoring the entry and element counts to avoid a structure full condition, take into account the reserved entries and elements used by the coupling facility.