RAC performance tuning issue

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RAC performance tuning issue

Postby hongying dong » Tue Oct 16, 2012 2:04 am

Tim,
when I tried to find info about hugepage, oracle-base.com poped up on the top list. I am so glad to know you are export on hugepage.
Our env. is 11gr2 RAC, 4 nodes and we use hugepage to help the 10tb import process.
1. we have 135gb RAM on OS which is RHEL
2. instance SGA_max_size is 70gb, other sga and mem params are set to enable hugepage
3 we have HugePages_Total: 34305, HugePages_Free: 705 HugePages_Rsvd: 705 Hugepagesize: 2048 kB, this come up to 68gb hugepage size
4. summarize all above, the total size of hugepage = SGA_max_size +7gb
5. OS always have 77 gb RAM in use which is size of hugepage, also I think hugepage ping them in memory, right?.

Here is my question,
1. I always watch the total of ram in use, it never gets over 77gb, no matter I have big load to database or not. sga_max_size takes 70gb in this RAM, so it only have 7gb for other processes. sometimes I saw database wait time is 99%, it mean database is hung, why can't use more RAM on OS, that is not fair, right?
2. I always puzzled by this 135 gb RAM on OS, why only 77gb RAM in use, what does stop using more RAM when needed?
3. I thought to increase the size of kernel.shmmax, but you told me not to do so. I agreed on this param, but which param can be used to max RAM usage?

thank you so much.
RB
hongying dong
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Re: RAC performance tuning issue

Postby Tim... » Tue Oct 16, 2012 1:00 pm

Hi.

The size of the memory you use is controlled by the instance parameters, like SGA_TARGET and PGA_TARGET. As soon as you start the instance this memory is allocated and doesn't increase or decrease. if you have told the instance to only use 70GB of RAM, then it's not surprising it is only using 70GB of RAM.

If you want the instance to use more memory, lets say 100G, then change your hugepages configuration to allow you to have 100G of hugepages-backed memory, then change your DB instance parameter to use it. You can't blame Oracle for doing what you told it to do!

Perhaps you need to read the concepts manual before you play around with Oracle any more...

http://docs.oracle.com/cd/E11882_01/ser ... 89/toc.htm

Cheers

Tim...
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Re: RAC performance tuning issue

Postby hongying dong » Tue Oct 16, 2012 3:25 pm

Thanks Tim, this realy help. I will read info in this link shortly.
hongying dong
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Re: RAC performance tuning issue

Postby Tim... » Tue Oct 16, 2012 4:03 pm

:)
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Oracle ACE of the Year 2006 - Oracle Magazine Editors Choice Awards
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OCP DBA 7.3, 8, 8i, 9i, 10g, 11g
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