topic Re: SWAP SIze For oracle Database in Operating System - HP-UX

SWAP SIze For oracle Database

George Nikoloudis_1 — Wed, 21 Nov 2001 18:45:41 GMT

The oracle suggest the the swap size should be 2 time the physical memory of the server. My server has 8 GB of Memory. DO I really need 16 GB of swap or 6 GB are enough?

Re: SWAP SIze For oracle Database

Geoff Wild — Wed, 21 Nov 2001 18:50:26 GMT

Check this out:

http://docs.oracle.com/database_mp.html

We have V-Class with 12 GB of RAM and almost 24 GB of swap - but this was mainly due to SAP requirement.

Rgds...Geoff

Re: SWAP SIze For oracle Database

S.K. Chan — Wed, 21 Nov 2001 18:51:49 GMT

Everything you want to know about swap ..
(see attached doc)

Re: SWAP SIze For oracle Database

Craig Rants — Wed, 21 Nov 2001 18:52:36 GMT

George,
I have an Oracle database running on a N with 8GB Physical 8GB Swap. I think the important thing is the SGA (System Global Area) that your DBA assigns to oracle. That will affect the memory more than if you double the size of Physical memory for swap.

Just my thoughts.
C

Re: SWAP SIze For oracle Database

A. Clay Stephenson — Wed, 21 Nov 2001 18:58:36 GMT

Hi:

In general, if you have an Oracle server that is swapping more than just a little then your performance is going to be poor. Do a vmstat and look at the 'po' (Page Outs) columns. Ideally that number should be zero indicating no swap outs. Depending upon the OS version, 8GB may well be enough memory so that your machine never swaps. In that case you can get by with only a small amount of primary swap (e.g. 512 MB) and with swapmem_on=1 to enable pseudo-swap.

The old rule of 2-3x (4-6x if mirrored) memory for swap very seldom applies these days. It is especially bad to buy that much disk that you are never going to use. I do suggest that you mirror your swap. My favorite way to do this is a small amount of primary swap, about 1.5x memory of filesystem swap at very low priority. The filesystem swap is just there as a safety net and does not consume filesystem space unless actually needed. I then configure a 1x memory size of dump area that is not mirrored.

Regards, Clay

Re: SWAP SIze For oracle Database

Sanjay_6 — Wed, 21 Nov 2001 18:59:16 GMT

Hi George,

you may want to take a look at the thread below,

http://docs.hp.com/cgi-bin/otsearch/getfile?id=/hpux/onlinedocs/os/11i/mem_mgt.html&searchterms=swap%7cwhite%7cpaper&queryid=20011121-110212

Hope this helps.

Regds

Re: SWAP SIze For oracle Database

Andreas D. Skjervold — Thu, 22 Nov 2001 13:48:12 GMT

Hi
First:
You do NOT want your Oracle SGA to begin swaping as this seriously affects performance.

As a result from this you'll never need swap space when running a plain database server. (Other applications on the same machine might though!)

Therefore it is a waste to have to configure twice the ammount of swap.
The swap requirement comes from the fact that every process reqires swapspace to be able to start (even if it is not going to use it)

To resolve this you should set up pseudo swap on your system. This is done by setting kernel variable swapmem_on to "1".

This enables a process to allocate up to 75 % more swap space than there is infact on the system.

rgds
Andreas

Re: SWAP SIze For oracle Database

George Nikoloudis_1 — Thu, 22 Nov 2001 17:45:09 GMT

By setting the swapmem_on = 1 will get 75% more swap it this good?
Is there a parameter in init.ora where locks the SGA in Memory?
The SGA size is 1.3 GB what parameters should I check in KERNEL in order to check if the SGA can feet to memory and npt swapped?