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Shared Memory Area

Because an MSS-enabled enterprise server contains more types of object than a non-CICS enabled enterprise server, there are more objects to take into account when you are deciding how much space to allocate to the shared memory area.
Item Calculation
Remote systems
  • Number of sysids x 96
  • Number of sessions x 32
PCT Number of entries x 48
FCT Number of entries x 88 + (4 x number of split key components used)
DCT Number of entries x 48
PPT Number of entries x 48
Programs (load hold)1 Number active x (average length + 8)
TST Number of entries x 32
PLT Number of entries x (56 + (8 x average number of items in list))
JCT Number of entries x 48
ICE2 Number active x 64
AID3 Number active x 64
Getmain SHARED4 Number active x (average length + 8)
ENQ5
  • Number active x (24 + average argument length)
  • Number of processes waiting on ENQ x 16
CICS client requests6 (3270 data stream length + COMMAREA + TEUA + 64) x number of servers
1 Programs loaded as data with EXEC CICS LOAD
2 Interval Control Elements. Tasks scheduled for a particular time.
3 Automatic Initiate Descriptor. Tasks awaiting a free service execution process for execution.
4 Areas of memory allocated with EXEC CICS GETMAIN SHARED.
5 User controllable synchronization locks allocated with EXEC CICS ENQ.
6 The buffers calculation is a rule of thumb. Use the average data stream, COMMAREA, and TEUA sizes for the computation. This only works if your system is set up to incur a minimum amount of SEP queueing. The buffers calculation must exceed the maximum size of a single buffer; that is, one that contains maximum data, COMMAREA, and TEUA sizes.

Buffers are short lived and stay in shared storage only if no SEP is available to service the request. Once a SEP is dispatched, the buffer is immediately moved to local process storage and the shared storage is released. Outbound buffers also stay in shared storage for a very short period of time. Outbound, the only delay is for processor dispatch to the supporting terminal process. Once the terminal process is dispatched, the buffer contents are moved to local process storage and the shared storage buffer is released.

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