Blockset technique

The Blockset technique is DFSORT's most efficient method for sorting, merging, and copying. Blockset uses optimized algorithms and makes the most efficient use of IBM hardware. DFSORT uses Blockset whenever possible. DFSORT's other techniques, Peerage/Vale and Conventional, are not as efficient as Blockset and are only used when Blockset cannot be used.

The Blockset technique can reduce CPU time, I/O activity, and Elapsed time. It is strongly recommended that you remove any obstacles to using Blockset whenever possible. For the purposes of this document, any recommendations to improve performance assume that Blockset is the DFSORT technique used.

It is worth checking to see if Blockset was used for a given application; message ICE143I in the SYSOUT data set shows which technique was used. If ICE143I is not shown or shows that a technique other than Blockset was selected, resubmit the application with a SORTDIAG DD statement (unnecessary if the application already had a SORTDIAG DD statement or if your site has specified installation option DIAGSIM=YES). Additional DFSORT messages and diagnostic information are then shown, including:

ICE802I, which shows the technique used
ICE800I or error messages

ICE800I gives a code indicating why Blockset was not used. If the code is 1, one or more error messages are also shown.

Note: Blockset messages are suppressed if another technique is selected, unless a SORTDIAG DD statement is present, or installation option DIAGSIM=YES has been specified for your site.

Blockset will not be selected if you specify work data sets on tape devices. Blockset only supports tape devices for input and output data sets. It is very strongly recommended that you use disk rather than tape for work data sets.