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  • 1.  NUMTCB

    Posted 03/11/25 03:46 AM
    Edited by Soledad Martinez 03/11/25 08:11 AM

    Good day, 

    while reviewing the WLM environments at one system, I found one that is running with NUMTCB=5, it has an old remark saying that the WLM is for High Storage SP.

    I checked the SP assigned to it, and all of them have some LOB column, but there are others with LOB columns running at WLM environments with higher NUMTCB.

    At IBM site I can see that the recommended range is from 10 to 40 NUMTCB for SP written in  Cobol and C, and one of the ways to increase the perfomance of the Stored Procedures is increasing the NUMTCB,

    So, does make any sense to have a WLM with NUMTCB=5? Can this be an old configuration? Is there anybody who had to set the NUMTCB to something lower than 10 due to storage or any other problem?

    Thank you!

    #Db2, #Db2 for z/OS 



    ------------------------------
    Soledad Martinez
    Db2 z/OS System Programmer
    Volkswagen Group Services
    Salinas - Asturias
    ------------------------------



  • 2.  RE: NUMTCB
    Best Answer

    Posted 03/12/25 01:29 AM

    Hi!

     I have set NUMTCB=1 to limit the SPs to run "one at a time" due to DD card dependancies and I have vague memories of JAVA SPs that swallowed memory like it was going out of fashion, so I would guess it was those JAVA babies "back in the day" - Apart from limiting parallel running I can see no reason.

    Hope that helps!



    ------------------------------
    Roy Boxwell
    Senior Software Architect
    Software Engineering GmbH
    Duesseldorf
    +4921196149675
    ------------------------------



  • 3.  RE: NUMTCB

    Posted 03/12/25 03:39 AM

    Hello Roy, 

    yes, helps a lot of, coming from you it even helps "twice" :-)

    Thank you very much!



    ------------------------------
    Soledad Martinez
    Db2 z/OS System Programmer
    Volkswagen Group Services
    Salinas - Asturias
    ------------------------------

    Original Message


  • 4.  RE: NUMTCB

    Posted 03/17/25 09:28 AM

    Hi Roy, recommendation NUMTCB=1 for Java SP was due to Java SP did not support multi-threading, so every SP did run in its own JVM. This was changed in Db2 11 to one JVM per SP address space, support of 64 bit JVM and SP executed as Java threads. You can easily set it now to NUMTCB =25.  Checkout https://www.redbooks.ibm.com/abstracts/sg248180.html chapter 9.6.

    In general, NUMTCB for LE languages (Cobol/C etc) can be ~40. It depends on the typical concurrent executions and storage consumption which you should observe after making changes.



    ------------------------------
    Maryela Weihrauch
    ------------------------------

    Original Message


  • 5.  RE: NUMTCB

    Posted 03/12/25 08:46 AM

    I have always had NUMTCB=30 for our WLM address spaces that run Cobol and C, haven't experienced any problems.



    ------------------------------
    Will Smith
    ------------------------------



  • 6.  RE: NUMTCB

    Posted 03/12/25 11:57 AM

    Hello Will, 

    perfect, thay you so much for letting me know!  



    ------------------------------
    Soledad Martinez
    Db2 z/OS System Programmer
    Volkswagen Group Services
    Salinas - Asturias
    ------------------------------

    Original Message


  • 7.  RE: NUMTCB

    Posted 03/13/25 02:02 AM

    Vague memories of DB2 V6 with 2GB address spaces.   When were the SPs that use the environments created?

    Perhaps no longer relevant.



    ------------------------------
    James Campbell
    ------------------------------



  • 8.  RE: NUMTCB

    Posted 03/13/25 03:13 AM

    Good morning James, 

    they were created on 2011, long ago :-)

    I have found others with the MNSPAS parameter, that according to IBM:

    "If the environment is one in which the cost of starting new address spaces is very high, set the MNSPAS subsystem parameter to specify the minimum number of address spaces that are to be started and maintained."

    This MNSPAS was also added on 2011, and its remark refers the apar PM27097, I don't know if still starting a new address spaces is that costly.

    Thank you very much!



    ------------------------------
    Soledad Martinez
    Db2 z/OS System Programmer
    Volkswagen Group Services
    Salinas - Asturias
    ------------------------------

    Original Message


  • 9.  RE: NUMTCB

    Posted 03/13/25 08:57 AM

    The cost of starting a new address space isn't really about the system resources it takes. It's really more about can the application(s) calling the SPs afford to wait for a new address space to start. 

    With WLM cycling every 10 seconds, before it decides to start another WLM SP task, that 10 seconds could be costly to you.

    I've experienced slowdowns in applications and I could not afford to wait for WLM to react, so I use NUMTCB for certain address spaces to avoid this cost.

     



    ------------------------------
    Will Smith
    ------------------------------

    Original Message


  • 10.  RE: NUMTCB

    Posted 03/14/25 03:10 AM

    Good morning Will, 

    perfect, you are right, thanks for sharing your inputs!



    ------------------------------
    Soledad Martinez
    Db2 z/OS System Programmer
    Volkswagen Group Services
    Salinas - Asturias
    ------------------------------

    Original Message


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