Dynamically changing certain BPXPRMxx parameter values

These parameters specify maximum values: MAXPROCSYS, MAXPTYS, IPCMSGNIDS, IPCSEMNIDS, IPCSHMNIDS, IPCSHMSPAGES, and SHLIBRGNSIZE. You can use the SETOMVS or SET OMVS command to dynamically increase the current system setting, but if you specify a value that is too low or too high, you will get an error message. To use a value outside the range, you must change the specification in BPXPRMxx and reIPL.

While you can specify the SHRLIBMAXPAGES parameter to specify a maximum value, it will be accepted but will not have any impact on the system. The value that you specify will never be reached, because user-shared library objects are no longer supported.

To avoid specifying a value that is too low or too high, you can use a formula to calculate the maximum values. The minimum value is sometimes the current setting of the parameter and sometimes lower than that, as identified in the description of each parameter.

Example: The following example shows you how to perform the calculations using the IPCMSGNIDS parameter, which determines the highest number of unique message queues in the system. To use SETOMVS IPCMSGNIDS=xxx to increase the current setting, you must calculate the highest number that you can specify. According to the description of IPCMSGNIDS in IPCMSGNIDS and IPCSEMNIDS, the formula is:

MIN(20000,MAX(4096,3*initial value))

For this example, the current value of IPCMSGNIDS is 1000; the value of IPCMSGNIDS at IPL is also 1000 (that is, 1000 is the initial value). Use the formula in the following way:

Compare 4096 with 3 times 1000 to find the higher number (the MAX). 4096 is the higher number.
Compare 20000 with 4096 to find the smaller number (the MIN). 4096 is the smaller number.

Therefore, the highest number that you can specify on SETOMVS IPCMSGNIDS is 4096. The range of numbers that you can specify is 1000 (the current value) to 4096. The correct SETOMVS command for increasing the message queue limit to the maximum (assuming a starting value of 1000) would be:

SETOMVS IPCMSGNIDS=4096

To change to a number higher than 4096 (but lower than 20000), you will have to change BPXPRMxx and reIPL.