Db2

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  • 1.  DB2 Memory Utilization Different Under RHEL7 Versus RHEL8

    Posted Mon August 26, 2024 11:12 AM

    I am not a DBA, rather a Linux engineer. For reference, we are running 11.5.8.0 under RHEL8 and 11.5.7.0 under RHEL7.

    My question involves memory utilization by DB2 on RHEL7 versus RHEL8.

    Under RHEL7, DB2 immediately reserves process memory let's say ~300gb. Under RHEL8 though, it initially allocates much less, let's say ~50gb, but it does grow over time.

    Is this a RHEL difference, DB2 difference or both?

    Any ideas would be greatly appreciated.

    Thanks,

    Lou



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    Louis Gallo
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  • 2.  RE: DB2 Memory Utilization Different Under RHEL7 Versus RHEL8

    Posted Tue August 27, 2024 03:54 AM

    Hmm - your environment is almost the same - except different version of OS and different version of Db2 :-)

    For completeness - you should at least state your physical memory and Db2 data manager configuration settings; number of databases and which are activated at startup would be helpful too



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    Jan Nelken
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    Original Message


  • 3.  RE: DB2 Memory Utilization Different Under RHEL7 Versus RHEL8

    Posted Wed August 28, 2024 10:01 AM

    I have to agree with Jan Nelken.  There are many DBM configuration parameters which impact memory allocation.  To properly answer the question we would need to  compare the configurations.  If I had to guess, I would say the 11.5.7 instance is configured to allocate more memory.



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    Andy McLaughlin
    Great American Insurance
    Cincinnati
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    Original Message


  • 4.  RE: DB2 Memory Utilization Different Under RHEL7 Versus RHEL8

    Posted Thu August 29, 2024 02:48 AM

    Hi Louis,

    a quick Google bashing with 'rhel7 vs rhel8 memory changes' lead me to this article: https://access.redhat.com/solutions/7042476

    You might want to check explicit configured kernel parameters on both machines https://www.ibm.com/docs/en/db2/11.5?topic=pddsilu-kernel-parameters-db2-database-server-installation-linux-unix and especially vm.swappiness.

    You can check Db2's mem use with "db2pd -dbptnmem" on both machines.

    Hope this helps!

    Cheers



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    Roland Schock
    IBM Champion and IBM Gold Consultant
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    Original Message


  • 5.  RE: DB2 Memory Utilization Different Under RHEL7 Versus RHEL8

    Posted Tue September 03, 2024 04:44 AM

    I have seen many system admins worry about memory usage on DB2 LUW servers.
    This is because when a database is active bufferpools are allocated and DB2 can allocate memory as high as 97% memory utilized for all the memory parameters available.
    However when OS or other process needs the memory, DB2 usually gives some memory back and automatically tunes the memory using something called STMM(Self Tuning Memory Management). You can reduce the DB_MEM_THRESH value for the DBs and gain a little more memory if you are worried. We however consistently see servers with more than 95% memory used/allocated and run smoothly without any issues.



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    Bujji Phanikiran V
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    Original Message