FastSort Manual
Sorting Interactively
FastSort Manual—429834-003
2-12
Controlling Extended Memory
If your input files have different maximum record lengths, you might want to specify a
smaller segment size. You can use the average record length rather than the maximum
to compute the file size and then specify the smaller size in the SEGMENT parameter.
In a parallel sort, FastSort distributes input records to multiple processors and scratch
disks. In this case, if you specify a mode of AUTOMATIC or MINTIME, you limit the
extended memory segment for the distributor-collector SORTPROG process to 90
percent of the physical memory not locked down by the operating system. Specifying
MINSPACE limits the extended memory segment to 256 pages. The extended
segment size limit for each subsort process is the same as for serial sorting.
You can use the VLM option to increase the amount of extended memory available for
sorting. The maximum extended memory segment when VLM is on is 62,255 pages.
For an interactive sort, you use a SORT DEFINE to turn on VLM. For more information,
see Using VLM
on page 9-10. For more information about using a SORT DEFINE, see
Section 7, Using SORT and SUBSORT DEFINEs
.
FastSort clears the command specifications after a run. Therefore, these specifications
are in effect for only one run unless you save them. Use the SAVE and CLEAR
commands to perform consecutive runs that involve similar data records and the same
key fields. You can retain repeated information, and you can remove extraneous
commands quickly after each run.
Table 2-1. Extended Memory Used by FastSort
File Size, in Bytes
Parameter
No
Merge
Passes
One
Merge
Pass Extended Memory, in Bytes
MINSPACE
100 KB 512 KB
AUTOMATIC
100 KB
> 100 KB
512 KB
MINTIME
200 KB
> 200 KB
SEGMENT n
n = 256
n > 256
100 KB
512 KB
MIN = Minimum of two values in parentheses
MAX = Maximum of two values in parentheses
b = Scratch block size
f = File size in bytes (total input record count times maximum input record size)
n = Segment size in pages
MIN
bf
2
------------- 1 . 3 0.5MB
MAX f 1.3 512KB
MIN
bf
2
------------- 1 . 3 0.7MB
MIN n 2048 0.9MB