Oracle 9i uses almost 2 times that of Oracle 8i 32-bit

[Sushil Singh_1]

Hi all
Recently we upgraded from Oracle from 8i 32-bit to 9i 64-bit. All the background process are now using 2 twice the amount of memory as compared to Oracle 8i. We have more than 1000 shadow process which also show increase in memory utilization.

Currently we have 8400 with 16 CPU and 6 GB of RAM with 11i. All I want is better understanding why the increase and how should I be able to project the increase number of memory. We need to annouce it to our customer and need exact answer. I would appreciate any information or if someone can point me to the right location (documentation).

Thanks
Sushil Singh

[Bill Hassell · Accepted solution]

The reason to use a 64bit program is to remove memory address limitations. As with all performance questions, there is no exact answer, especially with Oracle. From a purely technical point of view, every memory reference instruction in the applications will be twice as large. But that is far too simplistic. If you want high performance, you'll want to increase the Oracle SGA significantly larger than it is right now.

As a 32bit app, Oracle could not easily address more than 950megs of RAM, a bit more if relinked with different options. But all 32bit apps occupy the same shared memory area. Your DBAs may wish to increase SGA to several gigabytes in which case 12Gb would be very useful. You can run your entire app in just 2Gb (with 10Gb of swap space) if you like, but paging (swapping) would degrade performance as much as 100:1.

You could leave the RAM as is and just monitor page out rates with vmstat. If the po column begins to hit double digits, you need more RAM. If it hits triple digits, you need to double RAM to maintain reasonable performance.

[Hein van den Heuvel]

Check out the following link for a prior discussion of this topic in this very forum:

http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=48089


Hein.

[Julio Yamawaki]

It's true that Oracle uses more memory for all background process in 9i.
In the case of ora_xxx processes, there are nothing that you can do.
In the case of oracle you can use shared servers to avoid using one server for one client and thus saving memory without sacrificing memory.

[Steven E. Protter]

You are lucky it didn't take more.

I think Bill's answer is the one to focus on. You want it to use more memory. It will provide you better, more reliable performance.

I would add that there are some bugs with resource locking in the Oracle 9i .0 releases. Before you go production you need to get the latest major oracle patch set in.

This patch set converts the data so it does require some downtime.

SEP

[Brian Crabtree]

Sushil,

I wouldn't worry about what the background processes show as being taken by memory. Overall, you are going to see the processes holding a larger amount of memory, however the memory shown is going to be part of the shared memory block that oracle itself is using.

The memory being taken by Oracle should not exceed your sga_max_size. One thing to note however, is that your pga_aggregate_target can grow if it is not set correctly (provided you are using this parameter, which I would recommend).

Thanks,

Brian

[Nicolas Dumeige]

Memmory management in Ora9i is very different from previous version.
Have you opted for manual or auto memmory management ?

The fact that Oracle has a larger adressable space doesn't mean that it's memmory usage will be double !!!

The difference you see lies in your setting, it is not an Oracle database design flaw.

I'm very suprise with all previous answers !

[Sushil Singh_1]

Hi guys
Thank you all for the response. Its was a great insite to my problem. I did little bit more digging and got the following.

Oracle 9i uses 1GB of Large Virtual Memory Page Size and in 8i it used 4 KB. By reducing the page size, I was able to reduce 16% of memory utilization. Going below certain number could increase CPU utiliazation.

Thanks again for great input
Sushl Singh