Calculating the storage requirement for the extended common service area
You need to calculate the approximate requirement for the extended common service area (ECSA).
Procedure
To estimate storage that is needed for ECSA (above the 16-MB line) for each DB2® subsystem:
- Start with 3 MB of ECSA for the base and the first 100 users.
- Start with 0.1 MB for IRLM.
- Add 1.9 MB for IRLM required trace buffers.
- Add 1.9 MB for IRLM optional trace buffers.
- Add 4 KB for each additional user.
Add 4 KB for each active
remote thread.
- Add 4 MB or more for instrumentation facility interface (IFI) buffers as requested by the monitoring programs.
- Add up to 1 MB for each concurrently
executing DB2 command.
What to do next
If you use the distributed data functions of DB2, you may find that you need more virtual storage. You can estimate how much your storage needs are likely to increase in the ECSA above the 16-MB line by adding the following amounts:
- 1 KB for each conversation
- 2 KB for each thread that uses distributed processing
- 1 KB for each DB2 site in your network
- 40 KB for code that relates to distributed processing
Specify this sum or a value that is larger than this sum as the second value of the CSA parameter of the IEASYSxx z/OS® logical PARMLIB member. The logical PARMLIB is usually referred to as SYS1.PARMLIB. Specifying values that are too high is preferable to specifying values that are too low; making your values too low can result in a need to IPL z/OS. For example, if the ECSA size is too small, z/OS places the global load modules and control blocks for DB2 in CSA below the 16-MB line instead of above it. This can cause problems with coexisting z/OS subsystems.
Distributed threads use extended system
queue area (ESQA) when they are paused. The amount of storage that
is used might vary depending on the z/OS release
that is used. Estimate 4 KB of ESQA for every active distributed thread.