HeapPools summary

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

• Cell Size — the size of the cell specified on the __ucreate() call
• Extent Percent — the cell pool percent specified on the __ucreate() call
• Cells Per Extent — the number of cells per extent. This number is calculated using the following formula:

  Initial Heap Size * (Extent Percent/100))/(8 + Cell Size)

  with a minimum of four cells.
• Extents Allocated — the number of times that each pool allocated an extent.
• Maximum Cells Used — the maximum number of cells used for each pool.
• Cells In Use — the number of cells that were never freed.
  Note: A large number in this field could 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 * (Cell Size + 8) * 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 __umalloc/__ufree 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 will be used for the last suggested cell size.

For more information about stack and heap storage, see z/OS Language Environment Programming Guide.