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Conference vaxaxp::vmsnotes

Title:	VAX and Alpha VMS
Notice:	This is a new VMSnotes, please read note 2.1
Moderator:	VAXAXP::BERNARDO

Created:	Wed Jan 22 1997
Last Modified:	Fri Jun 06 1997
Last Successful Update:	Fri Jun 06 1997
Number of topics:	703
Total number of notes:	3722

681.0. "Effects of setting MAXBOBMEM to high?" by CSC32::D_BROWN (Dave Brown CSC-VSG/INTDRV) Tue Jun 03 1997 17:18

    
    	AlphaVMS V7.1
    
    	I'm working with a customer who has 40% of his memory on his
    AlphaServer 2100A 4/275 allocated to VMS. This is causing him quite a
    concern because his Oracle performance suffers greatly in the resultant
    memory shortage.
    
    	We're trying to find out why VMS is allocating so much memory and
    the only possibility we've identified so far is that he has set
    MAXBOBMEM from its default of 1600 to 500000 per the Oracle
    documentation. Could this causing VMS to be taking such a high
    percentage of his 256.00Mb as soon as the system boots?
    
    	Thanks,
    
    	Dave

T.R Title User Personal
Name Date Lines

681.1 EVMS::KUEHNEL Andy K�hnel Tue Jun 03 1997 18:58 17

T.R	Title	User	Personal Name	Date	Lines
681.1		EVMS::KUEHNEL	Andy K�hnel	`Tue Jun 03 1997 18:58`	17
	The reason is most likely not the amount of memory you are allowing for buffer objects. While Oracle can use buffer objects on teh SGA, a vanilla V7.1 system doesn't support this yet. You should be able to verify this quickly in SHOW MEM: the actual buffer object usage should be very low. Oracle 7 uses memory resident sections to map the SGA. These pages are not backed by a page file or section file: they stay in memory. SHOW MEM displays these pages as "permanently reserved to OpenVMS. We plan to fix this for the next release... In summary: a 256 MB system may be too small to use this VLM feature, depending on the size of the SGA and what else is going on on the system. I don't know enough about Oracle, but I believe you can also select a pageable SGA. Sounds like your customer would be better off with this option - or with more physical memory.

    The reason is most likely not the amount of memory you are allowing for
    buffer objects.  While Oracle can use buffer objects on teh SGA, a
    vanilla V7.1 system doesn't support this yet.  You should be able to
    verify this quickly in SHOW MEM: the actual buffer object usage should
    be very low.
    
    Oracle 7 uses memory resident sections to map the SGA.  These pages
    are not backed by a page file or section file: they stay in memory.
    
    SHOW MEM displays these pages as "permanently reserved to OpenVMS.  We
    plan to fix this for the next release...
    
    In summary: a 256 MB system may be too small to use this VLM feature,
    depending on the size of the SGA and what else is going on on the
    system.  I don't know enough about Oracle, but I believe you can also
    select a pageable SGA.  Sounds like your customer would be better off
    with this option - or with more physical memory.