swap size, kernel parameter

[Nguyen Anh Tien]

My server has 16 GB. According to regulations swap size must be twice of physical memory (32GB)
but my server is limited in size of physical disk (FC disk 36 GB) and I think that swap size should not
be set over 16GB. any one can help me?
My server has install Oracle Enterprise 8.1.7 and Bea Tuxedo 8.1 what Kernel parameter should I take care?

[Sridhar Bhaskarla]

Hi,

Set swapmem_on to 1. It will enable pseudoswap which means 75% of the memory will be initially alloted for swap. It is only for reservation calculation purposes and it will not be really used. Configure 1GB of primary swap in any case. If the disk is 36GB and if you are not going to have another VG, then add another 7GB as secondary swap (make sure the priority is 0) and dump. That will make upto 150% which is more than enough and will cover any 'anomalies' presented by your application. If the root disk is lesser than 18GB, then try secondary swap from another disk.

Keep watching 'swapinfo -t' regularly and as soon as the total becomes around 85%, start planning for secondary swap.

Also, ensure that your dbc_max_pct and dbc_min_pct are set to 4% and 2% respectively.

Do not forget to have a mirror disk. It will make your life peaceful.

-Sri

[Steven E. Protter]

When you have a system like that there is no regulations.

The installation will require you to set a swap area on device equal to half of memory. That's probably all you'll need based on what you have posted that is all the swap you need.

You can analyze memory use after the system is set up. How much swap you actually use depends on how much load there is, hnow many oracle instances, how big are the SGA's and such.

I'm including a monitor script and I recommend you run the script set and watch for results.

Swap reserveration will happen, but if you see no paging you're okay.

See A.Clay Stephenson's various posts on this topic.

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