Guidelines for allocating sort work data sets with DD statements
- When you include DD statements in your JCL, pay particular attention to the WER124I message that the sort routine issues. This message describes whether you allocated excess or insufficient space for your sort work data sets.
- Allocate sort work data sets in units of cylinders.
- Allocate the first sort work data set as CYL(1,1), which ensures that the sort routine uses the file size estimate passed by BMC AMI Log Master. If you allocate too much space to the first sort work data set, the sort routine might choose an inefficient sort algorithm. If your job uses an incorrect sort algorithm, the job might perform poorly or terminate abnormally when it exceeds sort capacity.
- Allocate all sort work data sets on one device type, preferably the device with the fastest data transfer rate.
- If possible, allocate sort work data sets on different VOLSERs across different channel paths.
- Do not use VIO data sets for sort work data sets.
- Allocate enough sort work space in primary storage to contain all of the input data.
- Start by allocating four sort work data sets. Allocate more only if you must (because of problems in obtaining extents). If you allocate more than 12 sort work data sets, high overhead can degrade performance. This limit applies even if the sort routine accepts more than 12 sort work data sets.
- When you must sort a large volume of data (over one gigabyte), allocate four to twelve sort work data sets on separate devices, depending on the file size. If possible, allocate an equivalent number of channel paths for optimal performance.
- If your job has a very large sort (over two gigabytes) and performance and elapsed time are important, consider turning off dynamic allocation by specifying SORTDYN as USE and WORKOPTS NUM as 0 on the SORTOPTS statement. Use DD statements in your JCL to allocate the sort work data sets. Be sure to allocate enough space to process all of the data.
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