psuedo swap and oracle relationship

[Valarie Lim]

My system has 4GB of RAM. and Swap space is not an issue.

I have three instances of database, 1GB, 400MB and 14MB SGA size.

Understands that Oracle requires contiguous memory to startup a database.
I have no issue starting the 1GB db instance, but when it comes to the 400MB instance, oracle complains not enough memory.
Will turning off the psuedo swap increase the chances of having more contigous memory, since psuedo swap in my case is not really neccessary.
With this change, will it increase the probability of starting the remaining two instance of 400MB and 14MB.

Thanks!
Yew Meng

[John Palmer]

Hi,

No, turning off pseudo-swap will not 'increase your chances'.

Your problem is caused by the fact that you are using 32 bit Oracle and the system has alimit of 1.75Gb for shared memory.

If you can't upgrade to 64 bit Oracle then I suggest that you investigate Memory Windows (provided you are running HP-UX 11.00). There's an overview document on 11.00 servers at /usr/share/doc/mem_wndows.txt and lots of threads in this forum.

Regards,
John

[Valarie Lim]

john,

I understand your point of the max of 1.75Gb of shared mem.

but the thing is that
1Gb + 400MB + 14MB= 1.414GB share mem.

There is still a certain allowance from the limit of 1.75GB.

I am on K450 with 4CPU and 4GB of RAM running on HP-11.00 (32bits) due to limitation on the H/W.
Therefore I am stuck with Oracle 32bits.

FYI, when psudo swap is turn on, 3GB of MEM is allocated for psuedo swap. What is in always in use by the swap is actually 1.2GB out of 3GB.

Therefore if I turned off the psuedo swap, the 1.2GB possibly contiguous can be use for the oracle instance since I have yet to hit the 1.75GB limit.

Thanks!

[Andreas D. Skjervold]

Hi

Pseudo-swap does NOT USE any of your physical memory for swapping.
What pseudo-swap does is just to tell the system to not enforce such strict swap reservation rules as it esle would upon proces creation.
With this HP-UX is allowed to reserve more swap space than there infact is configured on the system (up to 75 % of physical memory)

Andreas

[John Palmer]

The 1.75Gb limit is for ALL processes using shared memory.

You can check what shared memory segments exist with ipcs -am.

According to Metalink, Oracle doesn't need contiguous shared memory, it can also operate in contiguous multi-segment, and non-contiguous multi-segment mode.

What version of Oracle are you using and what ORA error do you get?

Regards,
John

[Valarie Lim]

Thanks John!

I got your point.
The shared memory is actually for all processes. That is where I miss the point.

The system has a PRECISE process that takes up 400MB of share Memory.
which explains why the second instance of 400MB unable to startup.

FYI, my oracle is running 8.1.6. shmmax defined in the kernal is 600MB.
and in the ipcs -am, the 1GB db instance have two oracle entries, 600MB and 400MB.

John, Can we define the SGA size to be bigger than 1GB but leser than the 1.75GB limit.

I don't really get your point on the contigous multi segment and the non-contiguous multi-segment mode.
It will be great if you can elobrate slightly further or guide me to the relevant site for information.

Thanks!
Yew Meng

[Valarie Lim]

Thanks Printaporn for your time!

You have clarified a lot of my doubts and answered most of my questions.

Thanks!
Yew Meng