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Re: Oracle SGA size on i386 platforms

From: Tim X <timx_at_spamto.devnul.com>
Date: Sat, 09 Apr 2005 13:15:35 +1000
Message-ID: <877jjcy71k.fsf@tiger.rapttech.com.au>


"Dave" <x_at_x.com> writes:

> "Tim X" <timx_at_spamto.devnul.com> wrote in message
> news:87ekdmxl4m.fsf_at_tiger.rapttech.com.au...
>>
>> Hi All,
>>
>> Just wondering if I can get some clarification on SGA size limits in
>> Oracle 9i running on i386 based platforms (Windows and Linux). I've
>> been told there is a 2Gb limit on both these platforms - though there
>> does seem to be some workarounds under windows which will allow you to
>> get to 3Gb.
>>
> there is a 1.75 gb limit on 32bit systems, without some fancy relinking on
> linux or playing with windows
>
> no gotchas (hate that term) on windows, if you understand windows - will
> work well for you.
>
> Why do you think you need a bigger than 4gb SGA?

Thanks. its not certain we need a larger than 4Gb SGA. We are currently running a 4Gb SGA - originally we started with just 2Gb, but this has slowly been increased as we tuned the config. On the current platform, we cannot go above 4Gb because we are still running an 8i database on this system and to go above 4Gb, there are some OS config changes required that then prevent 8i from being able to run at all. However, our senior DBA would like to have the flexibility of being able to go higher - especially as there is some functionality in the app we have not yet enabled because we don't feel we currently have the processing power to support it.

Probably our biggest concern is that if we move to a 32bit platform, will we be able to get acceptable performance. The application we are running is not supported for Oracle RAC, so we cannot cluster the system (though they are promising both a RAC and AMD64 bit supported release by the 3rd quarter of 2006). However, we cannot wait until then as our current performance is unacceptable and having an adverse impact on the business.

We are currently running the application on an Alpha ES40. The server also has a number of other Oracle based apps, though they are quite low demand ones. The ES40 has 4 733Ghtz CPUs and 30Gb of memory. Our average load has gone from 5 prior to this new application to an average of around 50 with extended peaks of 70 to 80. Performance is unacceptable. Our analysis indicates the primary bottleneck is CPU based, not memory or disk i/o. With a 4Gb SGA we are getting excellent cache hit ratios and minimal disk i/o. The application also uses 9iASr2, but our analysis indicates this only has a negligable impact on the system.

Our plan is to move the DBMS onto either a windows or linux platform. The vendor does not support Linux at this time, but they do support windows. We would like to go to 64bit Linux running on a 4-way opteron, but if we want to stick with a supported platform, it has to be 32 bit windows and we are concerned about the impact of an SGA which will be less than half our current config.

Tim

-- 
Tim Cross
The e-mail address on this message is FALSE (obviously!). My real e-mail is
to a company in Australia called rapttech and my login is tcross - if you 
really need to send mail, you should be able to work it out!
Received on Fri Apr 08 2005 - 22:15:35 CDT

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