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File size and dynamic allocation z/OS DFSORT Application Programming Guide SC23-6878-00 |
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DFSORT bases the amount of work space it dynamically allocates
on the number of bytes to be sorted—the input file size. Generally,
DFSORT can automatically make an accurate determination of the file
size by determining the number of input records. However, DFSORT
cannot always determine the input file size accurately in the following
cases:
In these circumstances, if the number of
records is not supplied by the FILSZ or SIZE option, you will receive
message ICE118I. If dynamic allocation of work data sets is used,
DFSORT allocates the primary space according to the DYNSPC value in
effect. This can result in underallocation or overallocation, possibly
leading to wasted space or an out-of-space condition, respectively.
DFSORT will also allocate additional work data
sets with zero space that can be used to recover from an out of space
condition. The percentage of additional work data sets will be the
greater of 50% or the DYNAPCT value in effect. To avoid unknown file
size situations, you should specify FILSZ=En with a reasonably accurate
estimate of the number of records to be sorted. If you cannot specify
FILSZ=En, you should use DYNSPC=n to adjust the primary space for
dynamically allocated work data sets and DYNAPCT=x to increase the
number of additional work data sets, as appropriate.
Note: FILSZ=E0 is ignored.
For variable-length records, DFSORT uses one-half of the maximum record length (LRECL) in conjunction with the number of records to determine the input file size, unless you specify AVGRLEN=n. If your actual average record length is significantly different from one-half of the maximum record length, specifying AVGRLEN=n can prevent DFSORT from overallocating or underallocating dynamic work space. See OPTION control statement for more information about the AVGRLEN, DYNSPC, FILSZ, and SIZE options. |
Copyright IBM Corporation 1990, 2014
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