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Kernel Memory Usage

MaxDB Version 7.8.01.14

Operating System Wi Server Standard Edition, 64 Bit

Last Reboot 9 Dec 2011

We upgraded our MaxDB and SAP content Server last year about this time. Since then we have noticed that, when review Task Manger, the memory usage of the MaxDB kernel has increased to over 5 gig of memory when the server has been running for about 6 months. Back in December we reached a point where the content server stop responding so the system was rebooted. At that time the MaxDB kernal was using 5.8 GB of memory. After the reboot we dropped down to 300 MB. Yesterday we were performing some maintenance on the system and noticed that we have climbed back up to over 6 gig of memory for the MaxDB kernel.

We have searched notes and also on line, but have not been able to determine if there is a setting we should configure that would release memory when we reached a certain point. Or is the solution to reboot the server every so often to reset. I have attached the setting we currently have:

Thanks for the assistance

Capture.JPG (40.9 kB)
Capture.JPG (54.9 kB)
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  • Posted on Jun 19, 2012 at 08:06 PM

    Hi John,

    Refer to Notes:

    1128916: SAP MaxDB/liveCache heap management

    &

    1173395: SAP MaxDB Configuration

    The IO buffer cache is configured using the database parameter CACHE_SIZE (CacheMemorySize). The IO buffer cache includes the converter cache and the data cache of an SAP MaxDB database.

    The size of the IO buffer cache generally has the greatest influence on database performance. The larger the dimensions of the IO buffer cache, the fewer time-consuming hard disk accesses have to be executed..In a system that is up and running, it is best if all data can be processed without hard disk accesses, that is, in the data cache. However, this is not usually possible in the OLTP environment and BW environment.

    Generally, you must use the results of the Quick Sizer to configure the IO buffer cache for SAP liveCache technology. Further information about the Quick Sizer is available on SAP Service Marketplace: http://service.sap.com/quicksizing

    Note that the database also allocates heap memory in addition to the IO buffer cache. You can determine the overall memory consumption of an SAP MaxDB database using the information from the system table MEMORYALLOKATORSTATISTICS. For more information about this, see Note 1128916: SAP MaxDB/liveCache heap management.

    Hope this helps,

    Regards,

    Yashwanth

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    • Hi John,

      the database parameter CacheMemorySize is set to 5.775.360 KB (=5,51 GB) in the screenshot above. This means that the database kernel is allowed to use ca. 5,51 GB of ram for its caches plus it will allocate some more heap memory depending on the amount of (among others) tasks and volumes configured. So a total amount of 6 GB would not be surprising.

      Still, I would suggest to lower the CacheMemorySize (maybe to 5 GB) and then watch the system closely. If the database 'kernel' process memory usage still tops 6 GB, I would suspect a memory leak in our database code. In that case, please upgrade your database to the latest available release within 7.8 (7.8.02.29) and if that does not help, open a SAP message, so that we can connect directly and check.

      A very good start to monitor the memory usage is using the Database Analyzer, go to 'expert view' -> 'Filling' and then look at the 'Sysheap' column (the Database Analyzer is automatically active in MaxDB SAP systems, if this is a stand alone database, you have to activate the Analyzer manually first).

      Thorsten

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