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Oracle SGA size

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Oracle SGA size

Hello,

The Oracle installation manual says that the maximum allowable shared memory is 1.75GB. Does that apply to the maximum size of the SGA? Must the SGA be less than 1.75GB?
8 REPLIES
Stefan Farrelly
Honored Contributor

Re: Oracle SGA size


There have been a lot of long detailed answers to this question. Please search the forum archives for shared memory and you will find the answers you seek.
Im from Palmerston North, New Zealand, but somehow ended up in London...
John Palmer
Honored Contributor

Re: Oracle SGA size

Hi,

Yes if you are using 32 bit Oracle, No if you are using 64 bit Oracle.

As Stefan says, a forum search will give you several previous threads.

Regards,
John

Re: Oracle SGA size

Does each instance of Oracle get it's own separate shared memory segment for an SGA or do all the instances' SGA's use only 1 shared memory segment?

For example:
Will this work for an HP11 Oracle 7.3.3.4 (32bit) database with 2 instances:
databaseA: SGA size set to 1GB
databaseB: SGA size set to 1GB.
Or does that exceed the 1.8G shared memory segment rule (assuming 4G swap and 4G physical memory)?

Thanks again!
John Palmer
Honored Contributor
Solution

Re: Oracle SGA size

Hi,

The 32 bit model for shared memory only allows 1.75Gb system wide.

However at 11.00, HP have implemented a system called 'Memory Windows' which allow many sets of 1.75Gb shared memory, each shared by a number of processes which are in the same 'window'.

For details, there are a couple of .txt files in /usr/share/doc (on an 11.00 system) called mem_mgt.txt and mem_wndows.txt.

Also a forum search will give you more information.

Regards,
John
CHRIS ANORUO
Honored Contributor

Re: Oracle SGA size

Hi,

Check the attached, it is from an ealrier posting done by Stefan.
I hope it helps.
When We Seek To Discover The Best In Others, We Somehow Bring Out The Best In Ourselves.

Re: Oracle SGA size

If there is a system wide limit of 1.75GB memory for 32 bit apps, why would HP sell a K570 HP10.20 system with 4G of memory? If what you say is true, wouldn't that other 2.25GB of memory be unusable?
John Palmer
Honored Contributor

Re: Oracle SGA size

You can use the rest for memory that is not shared.

Regards,
John
Alexander M. Ermes
Honored Contributor

Re: Oracle SGA size

Working with Oracle 32-bit the SGA is limited to 1.75 GB, even if you run several databases. If you do not use the 'Memory windows' of HP-UX, you are really in trouble.
That also counts, if you run several databases in 32-bit mode. Then you have to add up the size of the SGA's to avoid using more than 1.75 GB. Try to run Memory windows.
Kind regards
Alexander M. Ermes
.. and all these memories are going to vanish like tears in the rain! final words from Rutger Hauer in "Blade Runner"