FastSort Manual

Sorting in Parallel
FastSort Manual—429834-003
6-11
Specifying a Scratch Block Size
To improve performance for a parallel sort run on your system, you can specify one or
more of the following options in the RUN command or in the SORTMERGESTART
procedure:

The size of the I/O blocks for all scratch files

The size of the extended memory segment for the distributor-collector process and
for each subsort process

A location for the swap file for the distributor-collector process’s extended memory
segment

A copy of the licensed SORTPROG program in a location other than the
SYSTEM.SYSnn.SORTPROG file from which to run the distributor-collector
process

An execution priority for the distributor-collector process
Specifying a Scratch Block Size
The default scratch block size for each subsort process is 56 KB. The block size can
be any multiple of 2048 bytes up to 56 KB. You can specify a scratch block size by
using one of the following parameters:

The BLOCK parameter of the RUN command

The BLOCK parameter of the SUBSORT command

The scratch-block parameter of the SORTMERGESTART procedure

The BLOCK attribute of a SORT DEFINE
Any block size you specify applies to each subsort process. If there is a conflict
between block sizes specified in the SUBSORT and RUN commands, SORTPROG
uses the RUN command BLOCK parameter value.
Controlling the Size of Extended Memory Segments
Each SORTPROG process attempts to use enough memory to make only one merge
pass. For the distributor-collector process, the default maximum size of the extended
memory segment is 90 percent of the processor’s physical memory not locked down
by the operating system. For each subsort process, the default maximum size of the
extended memory segment is 50 percent of the processor’s physical memory not
locked down by the operating system. The minimum size for each process is 256 KB.
You can use the MINTIME, MINSPACE, or SEGMENT parameter to specify a different
extended segment size for the SORTPROG processes. If you specify the MINTIME
parameter, FastSort uses at most 70 percent of the physical memory not locked down
by the operating system. If you specify MINSPACE, the extended segment is only 256
KB. If you specify the SEGMENT parameter or the segment word, FastSort uses at
most only the number of pages you specify.