Overriding buffer definitions for HIOP

Each time you run the IMS Queue Control Facility functions by using ISPF panels or issuing JCL job streams, a buffer larger than 32 KB is required from the IMS high input/output pool (HIOP) for use by the IMS Queue Control Facility extensions, which run within the IMS control region.

This HIOP buffer is released when the IMS Queue Control Facility functions end processing. It is therefore recommended that you define a 64 KB HIOP buffer from a performance point of view because the use of oversized buffers is costly and IMS recommends avoiding oversized traffic.

While the IMS control region is being started, IMS Queue Control Facility checks whether a 64 KB HIOP buffer is defined. If not, it issues warning message IQC6221W, and the startup processing continues.

If IQC6221W is issued, you might want to override HIOP pool definitions by either of the following methods and then restart IMS to make the changes effective:

If the DFSSPMxx member of the IMS PROCLIB data set does not exist, or if DFSSPMxx exists but no HIOP buffers are not defined, add all of the following lines to DFSSPMxx:
```
FPL=HIOP,(256,64,32,N),(512,64,32,N),(1024,32,16,N)
FPL=HIOP,(2048,32,16,N),(4069,16,8,N),(8192,8,4,N)
FPL=HIOP,(16K,4,2,N),(32K,4,2,N),(64K,4,2,N)
```
If the DFSSPMxx member of the IMS PROCLIB data set exists and an HIOP buffer of a size other than 64 KB is defined, add the following line to add a 64 KB HIOP buffer:
```
FPL=HIOP,(64K,4,2,N)
```

For more information about the DFSSPMxx member of the IMS PROCLIB data set, see the topic "DFSSPMxx member of the IMS PROCLIB data set" in IMS System Definition.

Note: You can run IMS Queue Control Facility functions without a 64 KB HIOP buffer defined. If performance tuning of IMS Queue Control Facility functions is not necessary, you can ignore the warning messages.