DSM and DSMWEND Options - mfx - 3.1

The DSM and DSMWEND options allow you to control local DSM and to set an optimization mode.

MFX provides its best performance when global DSM is used instead of local DSM. For this reason, you should use local DSM only when processing requirements are unusual. For more information about local and global DSM, see Dynamic Storage Management (DSM) in the section Installation Consideration. In addition, you should change the delivered default that controls local DSM only under special circumstances.

DSM and DSMWEND also allow you to set an optimization mode for MFX. Normally, you would use the delivered default setting, which provides for a balance among CPU time, elapsed time, and I/O activity. However, in certain circumstances, you may want to direct MFX to minimize one of these resources at all times or during specific time intervals. For example, you can direct MFX to minimize elapsed time during the hours when your batch window is in effect and balance the use of all resources throughout the rest of the day.   

The DSM (valid Monday through Friday) and DSMWEND (valid on weekends) options have five positional subparameters (subp₁, etc.) If you omit any of the optional subparameters, you must remember to include the positional comma.   

The first two DSM and DSMWEND subparameters (subp₁ and subp₂) define a time interval. hh represents an hour value from 00 to 23. mm represents a minute value from 00 to 59. If you are setting parameters for local DSM, the DSM facility will be active for the entire minute specified in mm.   

The time interval begins at hhmm of subp₁ and ends at hhmm of subp₂. A maximum of five intervals may be specified, and one interval can cross a day boundary (for example, from 8 p.m. to 8 a.m. on weekdays). Time periods cannot overlap.   

The third subparameter (subp₃) has been superseded by the functionality of the fifth subparameter. The third subparameter is accepted but ignored.   

The fourth subparameter (subp₄) describes the optimization mode that MFX will use during the time period specified. This optimization mode will be used regardless of whether local or global DSM is enabled.   

The values that can be specified in the fourth subparameter are BALANCE, CPU, ELAP, and IO:   

BALANCE - Provides the best overall balance of CPU time, sort elapsed time (wall clock time), and I/O activity to SORTIN, SORTOUT, and SORTWORK.   

CPU - Minimizes the CPU time of each sort at the expense of sort elapsed time and I/O activity.   

ELAP - Minimizes the elapsed time (wall clock time) of each sort at some expense of CPU time.   

IO - Minimizes the amount of I/O activity (EXCPs) that a sort will perform.   

The fifth sub-parameter (subp₅) specifies the STGPCT value, which is the maximum percentage of available storage a sort can utilize. If this parameter is omitted, then for all optimization modes other than ELAP a default value of 30% will be used. For the ELAP optimization mode a default value of 40% will be used. If a value is specified, it will be used for all optimization modes. The valid   values   are   from 1 to 95. This value can be overridden   at run time by using the STGPCT runtime parameter.   

Here is an example of how you would direct MFX to minimize elapsed time and use up to 50% of available storage during the hours between midnight (0000) and 6 a.m. (0600) and balance the use of all resources and use the default 30% of available storage throughout the rest of the day (0601 to 2359) on weekdays (Monday to Friday):   

Sample DSM Code   

DSM=((0000,0600,,ELAP,50),(0601,2359,,BALANCE))

If you wish to disable local DSM at all times, you can specify OFF in place of the first three subparameters. You can also then specify an optimization mode. The following example shows turning all DSM off and having the sort use the ELAP optimization mode.   

Sample DSM Code

DSM=(OFF,ELAP)