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oracle 8i memory requirements with many instances

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Jose Luis De Diego
Occasional Contributor

oracle 8i memory requirements with many instances

Hi all.

I'm trying to adjust the SGAs sizes in a multi instances machine enviroment, and calculating the memory requirements for it, but I don't find the 'pagesize' or system page size.

Any one helping me? Is there any other way of doing the estimate?
7 REPLIES
Don Morris_1
Honored Contributor
Solution

Re: oracle 8i memory requirements with many instances

System page size is almost always 4096 bytes (4K).

You can check to be sure by calling sysconf() with _SC_PAGESIZE or _SC_PAGE_SIZE.

A. Clay Stephenson
Acclaimed Contributor

Re: oracle 8i memory requirements with many instances

The page size is 4k.
If it ain't broke, I can fix that.
Bill Hassell
Honored Contributor

Re: oracle 8i memory requirements with many instances

Note: memory requirements will be heavily constrained if you aren't running 64-bit versions of Oracle. The 32-bit default is to run all Oracle instances in a single 3750 meg area which is used by all processes for shared libraries, memory mapped files and shared memory segments. Since this area can get fragmented very quickly, you may wish to size 250 meg SGA's but cannot get a 3rd or 4th instance to run ("no space") because there is no contiguous 250 meg section.

If you absolutely must use 32bit Oracle, look into memory windows to give each instance a clean, unshared area of memory. In general, large SGA's, when configured with big sort areas and file buffers) make Oracle run very fast.


Bill Hassell, sysadmin
maria paschali
Frequent Advisor

Re: oracle 8i memory requirements with many instances

Hi,

i was going through the posts from the last couple of days, and I am really glad someone asked this question. I have been having problems getting a thrid database up and running. Either though I didn't post the question, I'd like to thank you all for your explanations and what I need to look at.

Thanks
MP
Bill Hassell
Honored Contributor

Re: oracle 8i memory requirements with many instances

You might want to get the shminfo program to monitor memory fragmentation. Here's a useful link:

http://forums.itrc.hp.com/cm/QuestionAnswer/1,,0x1259039599eed5118ff40090279cd0f9,00.html

In general, high performance for Oracle (and Stbase and Informix...) mean gigabytes (8-12) of RAM. The kernel tuning possible with HP-UX has very little effect when compared to changes in the Oracle SGA config file. If you think in terms of 1000-2000 megs for SGA per instance, you'll be safe. Of course, this means 11.0 or higher for big RAM support.


Bill Hassell, sysadmin
Jose Luis De Diego
Occasional Contributor

Re: oracle 8i memory requirements with many instances

Hi Bill.

My machine is 64-bit.

And thanks you all for answering so fast and well.
Jose Luis De Diego
Occasional Contributor

Re: oracle 8i memory requirements with many instances

Finally,

I called sysconf(_SC_PAGE_SIZE) from the command line:

#getconf _SC_PAGE_SIZE
4096