Additional performance tuning recommendations

Tuning I/O

The single most important factor affecting performance in REORG PLUS is I/O processing. During typical reorganization processing, REORG PLUS reads and writes large amounts of data. To maximize I/O performance, REORG PLUS handles all of its own buffering and performs I/O operations at the lowest level possible. Doing so allows REORG PLUS to read or write several blocks of data with each I/O operation and permits REORG PLUS to prefetch subsequent data.

To avoid I/O queueing, allocate REORG PLUS data sets on separate channels and drives. If you do not have sufficient channels available, use separate drives and control units.

Because REORG PLUS I/O processing is primarily sequential, DASD caching provides no benefit. Avoid DASD caching because the overhead might slightly increase I/O processing time.

For more information that can help you tune your I/O processing, see Performance-considerations-for-buffer-installation-options and Performance-considerations-for-sort-processing-options.

Providing maximum virtual storage

Because each task requires virtual storage for processing, REORG PLUS balances the multiprocessing performed with the amount of virtual storage that is available. The primary use of virtual storage is for I/O buffers by either REORG PLUS itself or by BMCSORT.

REORG PLUS uses as much virtual storage as needed for each task. For the best performance, BMC recommends that you specify REGION=0M in the JOB or EXEC statement of the execution JCL. If your data center does not permit you to specify REGION=0M, specify the amount that allows the most virtual storage, both above and below the 16-MB line.

Using a region size that is less than optimal risks the following potential issues:

• Running less efficiently, which could result in additional CPU and elapsed time
• Encountering memory failures or jobs that fail when new versions implement changes that require additional memory

If you specify a value for REGION other than 0M, ensure that you have an appropriate value set for the MEMLIMIT parameter, either as your site’s default SMF option or on your JOB statement or EXEC statement. BMC makes the following recommendations for the MEMLIMIT option:

• Specify NOLIMIT to allow unlimited above-the-bar memory.
• If you are unable to specify NOLIMIT, specify at least 4 GB; if you are reorganizing LOB or XML data, specify at least 32 GB.

Selectively redefining VSAM data sets

You can use the DSRSEXIT user exit to selectively redefine each object. By not performing the VSAM DELETE/DEFINE process for an object, you can significantly reduce elapsed and CPU time.