Common service area storage requirements

Some of the Db2 load modules and control blocks are in common storage. Most of the space is in the extended common service area (ECSA) and 64-bit common storage.

With few exceptions, the CSA-resident load modules are link-edited with the residency attribute of RMODE(ANY). Most of the modules reside in ECSA (above the 16 MB line of virtual storage), as do most of the global control blocks. The IRLM lock control blocks (RHB and RLB) use 64-bit private storage.

Monitor your use of CSA and ECSA, and increase those values if necessary. By monitoring CSA below the 16-MB line, you can determine whether you need to increase the size of the ECSA.

When you IPL z/OS®, you can override the CSA size with this syntax: 
CSA=(a,b)
where:
  • a is the number of kilobytes of CSA storage below the 16 MB line
  • b is the number of kilobytes of ECSA storage above the 16 MB line

The CSA value is rounded down to the next 1 MB boundary, while the ECSA value is rounded up to the next 1 MB boundary.

To define the size of the 64-bit common area, you can use the HVCOMMON parameter of the IEASYSxx member in the parmlib concatenation.

Db2 12 requires 64-bit common storage. Db2 requires that at least 6 GB of 64-bit common storage is defined for each Db2 subsystem that runs on a z/OS image.Additionally, the 64-bit common storage must be large enough to accommodate the size of the log buffers that is specified by the OUTBUFF subsystem parameter plus 15%.

Restriction: Ensure that you have defined a high enough value for HVCOMMON to satisfy requirements for all Db2 subsystems plus all other use on the LPAR. The default value is 66 GB. The 6 GB of 64-bit common storage that is requested for each member must be contiguous.