Application adjustments

The following are those cases for which you may want to adjust your application in order to take advantage of Hipersorting.

The Blockset technique was not selected. Hipersorting is supported only for the Blockset technique. If Blockset is not selected, message ICE800I indicates why it was not selected.
Note that the ICE800I message is printed only when a SORTDIAG DD statement was coded in the sort's JCL, or installation option DIAGSIM=YES has been specified for your site. Use the ICE800I reason code to determine the exact condition that is preventing the use of Blockset. If you are interested in using Hipersorting for the job, change your application appropriately to eliminate the particular condition, so that Blockset can be used.
Insufficient available virtual storage. In some cases, the amount of virtual storage available to DFSORT can influence the potential effectiveness of a Hiperspace. A Hiperspace of a certain size could be too small to improve performance when an insufficient amount of virtual storage is available, whereas the same size Hiperspace might be large enough to improve performance when a sufficient amount of storage is available. Since DFSORT does not use Hiperspace when doing so would not result in a performance benefit, insufficient virtual storage can indirectly prevent the use of Hipersorting.
Supply DFSORT with sufficient virtual storage if you would like Hipersorting to be used. The third value in message ICE092I or ICE093I indicates the amount of storage available for a particular sort job. To help reduce the likelihood of not using Hipersorting because of insufficient virtual storage, ensure that this value is at least the maximum recommendation given in Table 1. If necessary, increase the amount of virtual storage available to the job by specifying a larger MAINSIZE value on the OPTION control statement and/or raising the REGION value on the sort step EXEC statement.
Insufficient available central storage. The size of the input data set in relation to the total available central storage has an important effect on the performance of Hipersorting. If the size of the Hiperspace that could be created is too small to hold a significant percentage of the intermediate data, then the performance of the run would be degraded compared to using disk-only mode. Therefore, DFSORT chooses not to use Hipersorting in this situation.
If you would like Hipersorting to be used, there are several possible approaches you can take:
- Make sure that the HIPRMAX value or the installation IEFUSI exit is not limiting the application to a small amount of Hiperspace. Setting HIPRMAX=OPTIMAL (or to a very large value) and having IEFUSI allow at least 2 GB of Hiperspace per application will remove this limitation.
- Make sure that the EXPMAX, EXPOLD, and EXPRES values allow significant amounts of Hipersorting. This is accomplished by setting EXPMAX and EXPOLD to large values (or MAX) and EXPRES to a small value.
- Rerun the application when system activity, especially other concurrent Hipersorting and memory object sorting activity, is lower so that more storage is available for the sort. The more storage available, the larger the Hiperspace that can be created by DFSORT, and the larger the data set size for which Hipersorting can be allowed.
- In situations where business critical applications are executing concurrent with non-critical applications, it may be desirable to limit Hiperspace usage by a non-critical sort application to leave resources available for the business critical sort applications.
  
  Remember that some data sets are so large that Hipersorting can never be used to sort them, even if all of the storage installed on the system were available for the sort. To allow Hipersorting in such cases, you can either break up the large sort into multiple smaller sorts, or install more storage on the system.
- Reduce the size of the input data set, so that less storage is required for the sort. For some applications it is not necessary to sort all of the data, since only a subset is needed for processing. For example, INCLUDE, OMIT, SKIPREC, or STOPAFT can significantly reduce the amount of intermediate storage required by DFSORT. See z/OS DFSORT Application Programming Guide for more details about these features of DFSORT.
- Ensure that DFSORT has accurate information about the input file size. DFSORT can automatically estimate the file size for disk input data sets and tape data sets managed by DFSMSrmm or a tape management system that uses ICETPEX. However, there are certain situations, which DFSORT reports with message ICE118I, in which DFSORT cannot determine the file size. See "File Size and Dynamic Allocation" in z/OS DFSORT Application Programming Guide for more information on these situations, and what to do about them.
- The parameters that control the system resources manager (SRM) can indirectly affect the amount of storage that is available for all the jobs on your system, including sort jobs. For example, PWSS=(0,100) may cause DFSORT to not use Hipersorting. See z/OS MVS Initialization and Tuning Reference for information about SRM and its parameters.
Inefficient work data set usage. When a Hiperspace-mixed mode run is possible, DFSORT must decide how best to use both Hiperspace and disk work data sets. In most cases, trade-offs can be made such that both types of intermediate storage can be used efficiently. In some cases, however, it is impossible to use both Hiperspace and disk work data sets efficiently, in which case DFSORT chooses not to use Hipersorting.
In order to avoid such cases, use only 3390 or later model disks, and supply sufficient virtual storage to DFSORT, as described in Table 1. Sometimes, it is necessary to rerun the jobs when there is less system activity (to allow selection of Hiperspace-only mode) in order to take advantage of Hipersorting.

In general, DFSORT takes into account the potential effects of using Hiperspace on both the application's performance and the system's performance when determining whether or not to use Hipersorting. If either effect is not desirable, DFSORT chooses not to use Hipersorting.

See Memory object sorting, hipersorting and data space sorting for information on the benefits and operation of Hipersorting and Hipersorting, memory object sorting, and data space sorting for additional information on using Hipersorting effectively.