Shared Memory     (Overview)

DESCRIPTION
Sun MTP uses four different types of shared memory. This datapoint reports on 
the dynamic shared memory usage. Other types of shared memory are static and 
do not change during Sun MTP execution. The other types are Buffer Memory 
(also displayed on the Overview Screen), TCT Memory (based on the number of 
terminals defined) and Transaction Server memory (based on the number of 
Transaction Servers).  

Sun MTP allocates shared memory in blocks. The block size can be specified on
the command line to unikixmain with the -S option. The block size defaults to
128K. Sun MTP allocates blocks of shared memory as they are needed. After 
allocating the fifth block, Sun MTP attempts to double the block size for each 
subsequently allocated block. If Sun MTP cannot allocate the larger area, Sun MTP 
tries to allocate a block the same size as the last one. Sun MTP allocates up to
ten blocks of shared memory. 


VALUES
Sun MTPScan displays the amount of memory used (not allocated) in terms of Kbytes,
not blocks. Remember that the block size changes after the fifth allocation.


INTERPRETATION
The "Shared Memory" datapoint changes depending on:

 - the number of users that are logged on:  "Shared Memory" increases when users
   log on. When users log off, "Shared Memory" does not decrease. However, when 
   users subsequently log on to the system, the memory is reused and not wasted.

 - browse function usage:  "Shared Memory" increases when users Browse. When the
   function completes, Sun MTP returns the shared memory to the operating system.

 - temporary storage usage:  If temporary storage is not assigned to a file and
   the user utilizes temporary storage, "Shared Memory" increases. When the 
   temporary storage is no longer required, Sun MTP returns the shared memory to
   the operating system and "Shared Memory" decreases.


CONCLUSIONS
In most situations, the "Shared Memory" value should be equal to one or two 
times the value of the -S command line parameter to unikixmain to avoid running 
out of shared memory.  Remember that even if more shared memory is available
on the operating system, the Sun MTP system will only allocate a maximum of 10 
blocks.

However, be careful not to allocate too much shared memory with the -S option
if you aren't actually using it. The "Shared Memory" datapoint displays what you
actually use. If the amount of shared memory you use is substantially less than 
the amount allocated, you can decrease the initial block sizes with the -S 
option and free up a substantial amount of memory.

Sun MTP will fail to allocate shared memory if the operating systems shared memory 
configuration parameters are not set appropriately. These parameters are usually
called SHMMAX, SHMSEG and SHMMNI. Refer to the Sun MTP Administrators Guide for 
more information on how to determine appropriate values for these parameters.
