FastSort Manual

Sorting in Parallel
FastSort Manual—429834-003
6-13
Specifying an Execution Priority
Specifying an Execution Priority
The default execution priority for the distributor-collector process is the operating
system’s default priority for a process. You can use one of the following parameters to
specify a different priority:

The PRI parameter of the RUN command

The process-start parameter of the SORTMERGESTART procedure

The PRI attribute of a SORT DEFINE
Tuning and Testing a Configuration for Parallel
Sorting
For a large sort run, you can tune and test a configuration for the optimum
performance. To tune a configuration for a parallel sort run, follow these guidelines:

Place scratch files on different disk volumes and on separate volumes from input
and output files.

Select nonmirrored disks for subsort scratch files, if possible. A sort run is faster
with nonmirrored disks than with mirrored disks.

Unless you know the workload of all processors, let FastSort select them. FastSort
tries to put a subsort process in the same processor that is running the primary
disk process for the subsort scratch file volume.

Run the distributor-collector and each subsort process in different processors.
The most effective number and placement of subsort processes on your system
depends on the number and type of processors, the processor workloads, the number
and length of input records, and the type of output. To determine how many subsort
processes to use and where to run them, follow these steps:
1. Start with three subsort processes and use the automatic configuration.
2. Measure the performance using the Measure program. For more information, see
the Measure Reference Manual.
3. If the distributor-collector process is not at least 90 percent busy, add one or more
subsort processes. If the distributor-collector process is 100 percent busy, you
might need only two subsort processes.
4. Try to balance the subsort processes so that processors and disks have similar
rates of use. If a scratch disk is much busier than other disks, consider moving the
scratch file to another disk. If a subsort’s processor is being used more than other
processors, consider moving the subsort process to another processor.