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SWAP SIze For oracle Database

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George Nikoloudis_1
Frequent Advisor

SWAP SIze For oracle Database

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?
Geoff Wild
Honored Contributor

Re: SWAP SIze For oracle Database

Check this out:

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

Proverbs 3:5,6 Trust in the Lord with all your heart and lean not on your own understanding; in all your ways acknowledge him, and he will make all your paths straight.
S.K. Chan
Honored Contributor

Re: SWAP SIze For oracle Database

Everything you want to know about swap ..
(see attached doc)
Craig Rants
Honored Contributor

Re: SWAP SIze For oracle Database

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.
"In theory, there is no difference between theory and practice. But, in practice, there is. " Jan L.A. van de Snepscheut
A. Clay Stephenson
Acclaimed Contributor

Re: SWAP SIze For oracle Database


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
If it ain't broke, I can fix that.
Honored Contributor

Re: SWAP SIze For oracle Database

Andreas D. Skjervold
Honored Contributor

Re: SWAP SIze For oracle Database

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.

Only by ignoring what everyone think is important, can you be aware of what everyone ignores!
George Nikoloudis_1
Frequent Advisor

Re: SWAP SIze For oracle Database

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?