SET SYSTEM on z/OS

Use the MQSC command SET SYSTEM to dynamically change certain general system parameter values that were initially set from the system parameter module at queue manager startup. To permanently change these, either change the CSQ6SYSP parameters and regenerate the parameter module, or put the SET SYSTEM commands into a data set in the CSQINP2 concatenation.


Use MQSC commands

For information on how we use MQSC commands, see Performing local administration tasks using MQSC commands.

We can issue this command from sources 12CR. For an explanation of the source symbols, see Sources from which we can issue MQSC commands on z/OS .

Synonym: None


SET SYSTEM

SET SYSTEM DEFAULTparameter block CMDSCOPE(' ')CMDSCOPE(qmgr-name)1CMDSCOPE(*)1Parameter BlockACELIM(integer)EXCLMSG(character)LOGLOAD(integer)SERVICE(character)STATIME(integer)TRACTBL(integer)Notes:

  • 1 Valid only when the queue manager is a member of a queue sharing group.

The CTHREAD, IDFORE, and IDBACK parameters are ignored in IBM WebSphere MQ Version 7.1 or later, but are still allowed for compatibility with earlier versions. Any attempt to change the value of one of these parameters sets it to a default value of 32767.


Usage notes for SET SYSTEM

The new values take immediate effect, with the possible exception of STATIME and TRACTBL.

Changes to STATIME take effect when the current interval expires, unless the new interval is less than the unexpired portion of the current interval, in which case statistics are gathered immediately and the new interval then takes effect.

For TRACTBL, if there is any trace currently in effect, the existing trace table continues to be used, and its size is unchanged. A new global trace table is only obtained for a new START TRACE command. If a new trace table is created with insufficient storage, the old trace table continues to be used, and the message CSQW153E is displayed.


Parameter descriptions for SET SYSTEM

    CMDSCOPE
    This parameter applies to z/OS only and specifies how the command runs when the queue manager is a member of a queue sharing group.

      ' '
      The command runs on the queue manager on which it was entered. This is the default value.

      qmgr-name
      The command runs on the queue manager you specify, providing the queue manager is active within the queue sharing group.

      We can specify a queue manager name, other than the queue manager on which it was entered, only if we are using a queue sharing group environment and if the command server is enabled. We cannot use CMDSCOPE( qmgr-name) for commands issued from the first initialization input data set, CSQINP1.

      *
      The command runs on the local queue manager and is also passed to every active queue manager in the queue sharing group. The effect of this is the same as entering the command on every queue manager in the queue sharing group.

      We cannot use CMDSCOPE(*) for commands issued from CSQINP1.

    DEFAULT
    Resets all the general system parameters to the values set at queue manager startup.


Parameter block

For a full description of these parameters, see Use CSQ6SYSP.

Parameter block is any one or more of the following parameters that we want to change:

    ACELIM
    Specifies the maximum size of the ACE storage pool in 1 KB blocks. The number must be in the range 0-999999. The default value of zero means no imposed constraint, beyond what is available in the system.

    We should only set a value for ACELIM on queue managers that have been identified as using exorbitant quantities of ECSA storage. Limiting the ACE storage pool has the effect of limiting the number of connections in the system, and so, the amount of ECSA storage used by a queue manager.

    Once the queue manager reaches the limit it is not possible for applications to obtain new connections. The lack of new connections causes failures in MQCONN processing, and applications coordinated through RRS are likely to experience failures in any IBM MQ API.

    An ACE represents approximately 8% of the total ECSA required for the thread-related control blocks for a connection. So, for example, specifying ACELIM=5120 would be expected to cap the total amount of ECSA allocated by the queue manager (for thread-related control blocks) at approximately 64000K; that is 5120 multiplied by 12.5.

    In order to cap the amount total amount of ECSA allocated by the queue manager, for thread-related control blocks at 5120K, an ACELIM value of 410 is required.

    We can use SMF 115 subtype 5 records, produced by statistics CLASS(3) trace, to monitor the size of the 'ACE/PEB' storage pool, and hence set an appropriate value for ACELIM.

    We can obtain the total amount of ECSA storage used by the queue manager, for control blocks, from SMF 115 subtype 7 records, written by statistics CLASS(2) trace. The total amount of ECSA storage used is the sum of the QSRSPHBGF and QSRSPHBGV fields.

    For more information about SMF 115 statistics records, see Interpreting IBM MQ performance statistics.

    Note that, we should consider setting ACELIM as a mechanism to protect a z/OS image from a badly behaving queue manager, rather than as a means to control application connections to a queue manager.

    EXCLMSG
    Specify a list of message identifiers to be excluded from being written to any log. Messages in this list are not sent to the z/OS console and hardcopy log. As a result using the EXCLMSG parameter to exclude messages is more efficient from a CPU perspective than using z/OS mechanisms such as the message processing facility list and should be used instead where possible. This list is dynamic and is updated using the SET SYSTEM command.

    The default value is an empty list ( ).

    Message identifiers are supplied without the CSQ prefix and without the action code suffix (I-D-E-A). For example, to exclude message CSQX500I, add X500 to this list. This list can contain a maximum of 16 message identifiers.

    To be eligible to be included in the list, the message must be issued after normal startup of the MSTR or CHIN address spaces and begin with the one of the following characters E, H, I, J, L, M, N, P, R, T, V, W, X, Y, 2,3, 5, 9.

    Message identifiers that are issued as a result of processing commands can be added to the list, however are not excluded.

    For example: 
    SET SYSTEM EXCLMSG(X511,X512)
    suppresses the channel started and channel no longer active messages.

    LOGLOAD
    Specifies the number of log records that IBM MQ writes between the start of one checkpoint and the next. IBM MQ starts a new checkpoint after the number of records that you specify has been written.

    Specify a value in the range 200 through 16 000 000.

    SERVICE
    This parameter is reserved for use by IBM.

    STATIME
    Specifies the interval, in minutes, between consecutive gatherings of statistics.

    Specify a number in the range zero through 1440.

    If you specify a value of zero, both statistics data and accounting data is collected at the SMF data collection broadcast.

    TRACTBL
    Specifies the default size, in 4 KB blocks, of trace table where the global trace facility stores IBM MQ trace records.

    Specify a value in the range 1 through 999.

    Note: Storage for the trace table is allocated in the ECSA. Therefore, we must select this value with care.

Parent topic: MQSC commands