HEAPPOOLS summary

The HEAPPOOLS summary displays a report of the HEAPPOOLS statistics and provides suggested percentages for current cell sizes as well as suggested cell sizes.

• Specified Cell Size — the size of the cell specified in the HEAPPOOLS runtime option
• Element Size — the size of the cell plus any additional storage needed for control information or to maintain alignment
• Extent Percent — the cell pool percent specified by the HEAPPOOLS runtime option
• Cells Per Extent — the number of cells per extent. This number is calculated using the following formula, with a minimum of four cells:

  Initial Heap Size * (Extent Percent/100))/(Element Size)

  Note: Having a small number of cells per extent is not suggested because the pool can allocate many extents, which causes the HEAPPOOLS algorithm to perform inefficiently.
• Extents Allocated — the number of times that each pool allocated an extent.

  To optimize storage usage, the extents allocated need to be either one or two. If the number of extents allocated is too high, increase the percentage for the pool.

• Maximum Cells Used — the maximum number of cells used for each pool.
• Cells In Use — the number of cells that were never freed.

  A large number in this field can indicate a storage leak.

• Suggested Percentages for current Cell Sizes — percentages calculated to find the optimal size of the cell pool extent. The calculation is based on the following formula:

  (Maximum Cells Used * (Element Size) * 100) / Initial Heap Size
  With a minimum of 1% and a maximum of 90% 

  Make sure that your cell pool extents are neither too large nor too small. If your percentages are too large then additional, unreferenced virtual storage will be allocated, thereby causing the program to exhaust the region size. If the percentages are too small then the HEAPPOOLS algorithm will run inefficiently.

• Suggested Cell Sizes — sizes that are calculated to optimally use storage (assuming that the application will __malloc/__free with the same frequency).
  Note: The suggested cell sizes are given with no percentages because the usage of each new cell pool size is not known. If there are less than 12 cell sizes calculated and the last calculated cell size is smaller than the largest cell size currently in effect, the largest cell size currently in effect is used for the last suggested cell size.

For more information about stack and heap storage, see z/OS Language Environment Programming Guide for 64-bit Virtual Addressing Mode.