The primary goal for systems with limited memory space is to apportion available pageable main memory efficiently, according to the specific weight of the categories (NPP = number of pageable pages).
Memory capacity is limited if there are INACTIVE READY TASKS despite the fact that reasonable MPL values have been set (report “Active and inactive tasks for category” in the report group CATEGORY-QUEUE of SM2).
If this condition has never occurred during operation, the reader can skip this section and concentrate on the "Assigning priorities".
For PRIOR to be able to react flexibly to slight variations in workload, the working set requirements of the tasks, as represented by the sum of the MIN MPL values for all categories should be: (between 0.3 and 0.5) * NPP. The choice of the factor (0.3 or 0.5) depends on the emphasis desired for the application involved (see below).
Guidelines for the average working set requirements (4KB pages):
TP tasks:
WSTP = 200 to 400 pages for UTM and DCAM tasks
WSTP = 500 to 1.000 pages for DB tasks
Dialog tasks:
WSDIAL= 50 to 150 pages
Batch tasks:
WSBATCH = 50 to 200 pages
The working set for system routines and common memory pool, which are called by application programs, are managed globally in the SYS category (placeholder is TSN=PGE).
Category SYS:
WSSYS= 2,000 to 4,000 pages
See the ACTIVITY report of SM2 for the NPP value.
Main application: TP
Background application: dialog, batch
TP category
This category contains the tasks which place the greatest demands on performance. It is not desirable to limit the workload of this category, even in the event of overload. Therefore the value of MAX MPL must be equal to the total number of TP tasks in the system (including management tasks such as Data Base Administrator, etc.).
The value for MIN MPL should correspond to the desired number of active TP tasks. It is generally equal to or approximately equal to the MAX MPL value. If the value is too low and an overload occurs, this will cause TP tasks to be deactivated automatically (see section "Activating/deactivating tasks").
Recommended values:
MIN MPLTP = 0,8 * MAX MPLTP
MAX MPLTP = Total number of existing TP tasks
WEIGHT = 500
DIALOG category
This category is usually characterized by wide variations in workload. PRIOR attempts to reach the MIN MPL value set by systems support, if necessary by suppressing tasks in other categories (see section "Activating/deactivating tasks").
Since in this case the DIALOG application is meant to run in the background, the value of MIN MPL must not be too high.
Due to the effect of think time, not all dialog tasks are active at the same time. The number of active dialog tasks can be estimated with the aid of the following formula:
Number of active dialog tasks =
N = (Average think time + Response time) / Average response time
Guidelines:
Average think time (incl. network runtime) = 16 seconds
average response time = 4 seconds
N = 20 s / 4 s = 5
In order to calculate the MIN MPL value it is essential to know how much pageable main memory (according to the formula 0.5 * NPP with the emphasis on TP mode) is available for active dialog tasks after subtracting the working set requirement of the main application, the SYS category or, if applicable, of any necessary batch tasks for active dialog tasks (see example).
The value of MAX MPL is conceived as a workload limit for temporary overload situations. It should be set to twice the value of MIN MPL.
Recommended values:
MIN MPLDIAL = (0,5*NPP - (MIN MPLTP * WSTP + MIN MPLBATCH * WSBATCH + WSSYS)) / WSDIAL
WSTP: average working set requirements per TP task
WSDIAL: average working set requirements per dialog task
WSBATCH: average working set requirements per batch task
WSSYS: average working set requirements for system routines and common memory pools
Note
At this point it is only necessary to take the BATCH portion into account if, for operational reasons, a certain minimum number of parallel batch tasks is absolutely necessary for the corresponding IT installation.
MAX MPL = 2 * MIN MPL
WEIGHT = 100 (50 < WEIGHT < 200)
BATCH category
Normally, batch tasks are run in the background in order to make use of the free resources. In this case, the value of MIN MPL is derived from the size of pageable main memory (more precisely 0,5 * NPP) minus the working set requirement for the main application TP, the DIALOG application and the SYS category.
The value of MAX MPL varies according to the system workload, and should not deviate markedly from the value of MIN MPL.
Recommended values:
IN MPLBATCH = (0,5*NPP - (MIN MPLTP * WSTP + MIN MPLDIAL * WSDIAL + WSSYS)) / WSBATCH
MAX MPL = MIN MPL + 1
WEIGHT = 10 (1 < WEIGHT < 50)
Example for main application TP
MM = 64 MB
Main application TP:
6 UTM tasks, working set for each 300 pages
2 DB tasks, working set for each 800 pages
2 further tasks, working set for each 250 pages
Background application:
10 dialog tasks, working set for each 150 pages
At least 2 batch tasks, working set for each 100 pages
TP category:
MIN MPLTP=8
MAX MPLTP=10
WEIGHT=500
DIALOG category:
Number of active dialog tasks = total number of dialog tasks / N = 2
MIN MPLDIAL=2
MAX MPLDIAL=4
WEIGHT=100
BATCH category:
MIN MPLBATCH=2
MAX MPLBATCH=3
WEIGHT=10
64 MB = 16,000 pages, resident MM requirement = 1500 pages, i.e. NPP = 14,500 pages.
(MIN MPLTP * WSTP) + MIN MPLDIAL * WSDIAL + MIN MPLBATCH * WSBATCH + WSSYS <= 0,5*NPP
(6*300+2*800) + 2*150 + 2*100 + 2000 = 1800+1600+300+200+2000 = 5900
<=0,5*14500 = 7250
Main application: Dialog
Background application: TP, batch
TP category
The fact that the TP application appears as a background application does not necessarily imply that minimal or even no demands are placed on performance; it only means that the number of TP transactions is less than 50% of the total number of transactions.
This is always the case whenever new TP applications are introduced and the number of terminal users employing the new procedure is still relatively small. Since a single TP task always serves several terminal users, and also normally has greater working set requirements as compared to dialog tasks, it is generally not desirable to have TP tasks automatically deactivated in the event of overload.
Therefore, the value of MAX MPL should likewise be equal to the total number of TP tasks in the system. Similarly, the value of MIN MPL should be equal or approximately equal to the value of MAX MPL.
Recommended values:
MIN MPLTP2 = 0,8 * MAX MPLTP
MAX MPLTP2 = total number of TP tasks
WEIGHT = 500
DIALOG category
If the emphasis of the application lies on the DIALOG side, this entails higher demands on main memory with respect to paging intensity (see section "Examining system performance with openSM2") as compared to TP applications.
Therefore, the working set requirements of the tasks as represented by the sum of the MIN MPL values of the TP, DIALOG and BATCH categories should be <= 0.3 * NPP.
For calculating the MIN MPL value, it is essential to know how much pageable main memory (according to the formula 0.3 * NPP with the emphasis on DIALOG mode) is available for active dialog tasks after subtracting the working set requirements of the TP tasks, the SYS category or necessary batch tasks for active dialog tasks (see example).
Here, too, the number of active dialog tasks (initial estimation) should be set to
Number of active dialog tasks =
Recommended values:
MIN MPLDIAL=(0,3*NPP - (MIN MPLTP * WSTP + MIN MPLBATCH * WSBATCH + WSSYS)) / WSDIAL
Note
At this point, it is only necessary to take into account the BATCH portion if, for operational reasons, a certain minimum number of parallel batch tasks is required.
MAX MPL = 2 * MIN MPL
WEIGHT = (300 < WEIGHT < 500)
BATCH category
Given that batch tasks are running solely as a background workload, the following values apply:
MIN MPLBATCH = (0,3*NPP - (MIN MPLTP * WSTP + MIN MPLDIAL * WSDIAL + WSSYS)) / WSBATCH
MAX MPL = MIN MPL + 1
WEIGHT = 10 (1 < WEIGHT < 50)
Example for main application Dialog
MM = 64 MB
Main application DIALOG:
45 dialog tasks, working set for each 100 pages
BATCH:
At least 2 batch tasks, working set for each 100 pages
Background application:
2 UTM tasks, working set for each 200 pages
1 DB task, working set for each 500 pages
1 further task, working set for each 150 pages
TP category:
MIN MPLTP=3
MAX MPLTP=4
WEIGHT=500
DIALOG category:
Number of active dialog tasks = total number of dialog tasks / N = 9
MIN MPLDIAL=9
MAX MPLDIAL=18
WEIGHT=400
BATCH category:
MIN MPLBATCH=2
MAX MPLBATCH=3
WEIGHT=10
64 MB = 16,000 pages, resident MM requirement = 1500 pages, i.e. NPP = 14,500 pages.
(MIN MPLTP * WSTP) + MIN MPLDIAL * WSDIAL + MIN MPLBATCH * WSBATCH + WSSYS <= 0,3*NPP
(2*200 + 1*500) + 9*100 + 2*100 + 2000 = 400+500+900+200+2000 = 4000
<= 0,3*14500 = 4350
Main application: Batch
Background application: Dialog
This load is typical for night-shift operation of systems whose main memory is dimensioned for daytime online operation. As a rule, batch applications place a considerably lighter burden on main memory than online applications with regard to paging intensity; however, they put a far greater burden on the CPU.
The number of batch tasks that can be handled thus depends less on the main memory size than on the speed of the CPU.
The settings for the category parameters is of no significance here (the required load limitation can be specified using the job classes parameter CLASS-LIMIT).