The shared memory area is an area of memory where an enterprise server instance stores all the information it needs to run (see the section COBOL Server 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 enterprise server instance 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 instance.
Actual requirements vary according to the nature of the workload, but you are advised to allow a generous safety margin. Enterprise Server 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 |