A storage occupancy count measures the area under the curve of
user-task storage in use against elapsed time. The unit of measure
is the
byte-unit, where the
unit is equal to 1024 microseconds,
or 1.024 milliseconds. For example, a user task occupying 256 bytes
for 125 milliseconds is measured as follows (where
ms is milliseconds):
125 / 1.024 ms = 122 units * 256
= 31232 byte-units
Note: All references to
Start time and
Stop time in
the calculations below refer to the middle 4 bytes of each 8 byte
Start/Stop time field. The Start and Stop time fields are standard S/390® STCK time values where bit
51 of the Start time or Stop time represents a unit of 16 microseconds.
- To calculate the response time and convert into microsecond units:
Response = ((Stop time - Start time) * 16)
- To calculate the number of 1024 microsecond units:
Units = (Response / 1024)
or
Units = ((Stop time - Start time) / 64
- To calculate the average user-task storage used from the storage
occupancy count:
Average user-task storage used = (Storage Occupancy / Units)
- To calculate units per second:
Units Per Second = (1000000 / 1024) = 976.5625
- To calculate the response time in seconds:
Response = (((Stop time - Start time) * 16) / 1000000)
During the life of a user task, CICS® measures,
calculates, and accumulates the storage occupancy at the following
points:
- Before a storage GETMAIN request increases the current user-storage
values
- Before a storage FREEMAIN request decreases the current user-storage
values
- Just before a performance record is created for the user task.
Figure 1 shows a pictorial representation
of how the user storage occupancy measurement is calculated.
Figure 1. Transaction user
storage occupancy │ │
│←────────────────────────────────Response Time────────────────────────────────→│
│ │
S│ │S
T│ │T
A│ ┌───────────────────┐ │O
R│ │ │ ┌─────────┤P
T│ ┌────┐ │ │ ┌─────────┐ │ │
│....│....│....│...................│..............│.........│.........│.........│T
T│ │ └────┘ └────┐ │ │ │ │I
I│ │ . . . │ │ │ │ │M
M├────┘ . . . └─────────┘ └─────────┘ │E
E│ . . . . . . . . │
│ . . . . . . . . │
│ . . . . . . . . │
└───────────────────────────────────────────────────────────────────────────────┘
G F G F F G F G
G = GETMAIN
F = FREEMAIN
Dotted line = Average storage occupancy