OPTIMIZE EXTENT SIZING field (MGEXTSZ subsystem parameter)
The MGEXTSZ subsystem parameter controls whether secondary extent allocations for DB2®-managed data sets are to be sized according to a sliding scale. Sizing the secondary extents on a sliding scale optimizes the likelihood of reaching the maximum data set size before secondary extents are exhausted.
| Acceptable values: | YES, NO |
| Default: | YES |
| Update: | option 9 on panel DSNTIPB |
| DSNZPxxx: | DSN6SYSP MGEXTSZ |
- YES
- DB2 automatically optimizes the secondary extent allocations of data sets for table spaces and index spaces that have a SECQTY value of greater than zero. When all secondary extents are exhausted for the first data set of a nonpartitioned table space or a nonpartitioned index space that has a SECQTY value of greater than zero, the primary space allocation of each subsequent data set is the larger of the SECQTY setting and the value that is derived from the sliding scale algorithm.
- NO
- Secondary extent allocations are managed manually. For nonpartitioned table spaces and nonpartitioned index spaces, when all extents of the first data set are exhausted, the primary space allocation of each subsequent data set is always the PRIQTY setting.
When the sliding scale is used, secondary extent allocations that are allocated earlier are smaller than those allocated later, until a maximum allocation is reached. The maximum allocation is 127 cylinders for data sets with a maximum size of 16 GB or less, and 559 cylinders for data sets with a maximum size of 32 GB or 64 GB.
Secondary extent allocations for data sets in implicitly created table spaces are not influenced by this setting because they always use the sliding scale.
In migration mode, the input migration value for this field is overridden to YES, so you need to reset it to NO if you want to continue to disable secondary extent optimization.