MFX control statements can be used to eliminate records from the input file (INCLUDE/OMIT), obtain the minimum/maximum/sum/average of fields in equal-keyed records, and/or eliminate equal-keyed records (SUM or DUPKEYS), reformat records (INREC/OUTREC), set up multiple output files (OUTFIL) or write formatted reports (OUTFIL statement with HEADER, TRAILER, SECTIONS and OUTFIL parameters. These control statements provide a high performance alternative to the use of exits and invoking programs. The tasks they address are those which are most frequently executed and/or improve sort performance. Since sort throughput is in part a function of the number of bytes that are to be manipulated, considerable performance savings can result from using the INCLUDE/OMIT statement to eliminate irrelevant records; INCLUDE/OMIT affects the data set prior to sorting/merging/copying.
The SKIPREC and STOPAFT parameters are recommended for test runs of sorting applications for the same reason. When the file bias is high enough for a significant number of records to be summed early in the sort, SUM or DUPKEYS will also provide performance gains if the XSUM or XDUP option has not also been selected. When reformatting records, it is desirable to minimize the amount of data that must pass through the sort process. Other things being equal, INREC should be used to shorten records, OUTREC to lengthen them.