Shared Memory Area

The shared memory area is an area of memory where an enterprise server stores all the information it needs to run (see the section Server Enterprise Edition Architecture in the chapter Introduction). The shared memory area is measured in pages of 4KB each. The shared memory area has to be big enough to contain all the definitions of the objects in the server, and all the current client requests. If you run out of shared memory while the server is running, the performance of the server will be significantly affected and this could prevent client requests from being processed.

Use the calculation described in this section to estimate the number of shared pages to allocate to an enterprise server.

Actual requirements vary according to the nature of the workload, but you are advised to allow a generous safety margin. Server Enterprise Edition optimizes the use of the shared memory resource by minimizing the number of physical pages used at lower than maximum processing volumes.

Perform the calculations in the middle column of the table below and enter the result of each calculation in the right-hand column. The sum of these answers is the minimum number of bytes required for the shared memory. Divide this number by 4096 and round up to a whole number to get a figure for the number of shared pages needed.

Item Calculation Result
Overhead Fixed size 8192
Shared memory area management Shared memory area size / 4096  
Trace If auxiliary trace not active: Number of entries x 24  
Trace If auxiliary trace active: Number of entries x 24 x 11  
Local trace Number of service execution processes x number of entries x 24  
Services Number of services x (128 + service-name-length)  
Service execution processes Number of service execution processes x 144  
Request handlers Number of request handlers x (128+handler-name-length)  
Packages Number of packages x (128+IDT-name-length + application-path-length + module-name-length)  
Resident IDTs Number of resident IDTs x IDT-length  
Client requests Number of client requests being processed at any one time x (256 + average size of client request)  
Clients Peak number of concurrent clients x 64  
Access Control Environment Elements Peak number of signed-on users x 428

The number of signed-on users should include the 4 default users used by the system.

 
Total    

where:

service-name-length

is the length of the service name

handler-name-length

is the length of the name of the request handler

IDT-name-length

is the length of the IDT name

application-path-length

is the length of the path to the COBOL application in the package

module-name-length

is the length of the name of the module containing the application

IDT-length

is the size of the IDT file for a package