Setting a Kernel Parameter for Oracle 9i

[Tom Kreimer]

The setup for Oracle 9i wants me to set MAXSWAPCHUNKS to (available memory)/2.

Available memory is not a variable I can use in a formulat (like NPROC + 2), so what statistic to I use?

[Sanjay_6 · Accepted solution]

Hi Tom,

Looks like what is required is that if the RAM on your System is 4GB, you should set the parameter to 2GB.

Hope this helps.

Regds

[Tom Kreimer]

Sounds good. I was thrown by the word "available". I though that maybe it ment total memory minus some amount used.

[Don Morris_1]

maxswapchunks isn't in units of bytes --
and 2Gb is _way_ out of range for it anyway.

The important thing is that your _swap space_
is a certain value. swap_space = maxswapchunks * swchunk * usually 1Kb>

Most people recommend leaving swchunk alone unless you absolutely have to, especially if you want to do interleaving between devices with equal priority, and I tend to agree with them. So, if this is 11.11, swchunk is 2048 blocks -- so your swap space is maxswapchunks * 2Mb... which sounds linke what Oracle meant now that I do the math. :)

At any rate - if you want 4Gb of swap, then maxswapchunks should be set to 2 * 1024 = 2048 (units of chunks).

Don Morris

[Tom Kreimer]

This is 11.00 and SWCHUNK is indeed 2048, which is two 1Kb blocks I guess.

So if Oracle wants me to have a swap space equal to my available memory, I just divide available memory by 2 for MAXSWAPCHUNKS.

But what is "available" memory. Is it the same as physical memory (512Mb - This is a development system)?

Is it physical memory - system memory - user memory - chache memory (= free memory, currently 258.9Mb on my system) but isn't this a moving number?

The unit of value is not specified (most say Bytes), so I'm guess Kb here.

The current value is 4096, which is much lower than 512 *1024/2 = 262,144

[Patrick Wallek]

I would just use the total amount of memory in the machine. I wouldn't try to calculate the "available". That would bee too difficult, and, as you said, a moving target.

For definitive information on how to calculate you maximum amount of swap with the maxswapchunks parameter have a look at this page:
http://docs.hp.com/hpux/onlinedocs/os/KCparam.MaxSwapChunks.html

[Tom Kreimer]

The link to the documentation really helped. I'm sure that by "available memory" they mean "available swap space", which on my system defaults to 1GB.

So I'll change MAXSWAPCHUNKS from the default of 256 to 512, which is half of 1024Mb.

My current value of 4096 was probably set when I selected the "DB Server System" from "Tuned Kernel Paramter Sets" in SAM.