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SWAP Area Size & Kernel Parameters

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Shahbaz_1
Regular Advisor

SWAP Area Size & Kernel Parameters

Hi,
We are installing Oracle on HP - RP8400 Server,
What should be the ideal size of the "SWAP AREA" ?. The server has 6Gig of RAM.
And can I get the best value for "SHARED MEMORY" and semaphores?

Thanks & Regards
Syed
Let's share the great thing "THE KNOWLEDGE"
5 REPLIES
Steven Sim Kok Leong
Honored Contributor

Re: SWAP Area Size & Kernel Parameters

Hi,

The amount of swap is required depends on the number of Oracle server processes you are serving, the memory consumption for each individual server process and your SGA.

Because swap is usually configured as the dump device as well (unless you have it differently), you should have the swap space at least as large as the total memory on your system ie. 6 GB. This will allow your system crash dumps to be saved in completeness.

I suggest that you follow the recommended OS kernel parameters in the Oracle Installation Guide during the initial setup phase. With increased usage and load, monitor the performance over time and finetune your kernel parameters one at a time to see its impact.

Hope this helps. Regards.

Steven Sim Kok Leong
Email: steven@beepz.com. Homepage: https://www.beepz.com
Michael Tully
Honored Contributor
Solution

Re: SWAP Area Size & Kernel Parameters

Hi,

In the past having 2 x RAM = swap was normal.
That was in the days when memory cost so much.
These days if you have a system that has that
much RAM it can actually harm performance by
having too much swap. I would suggest you
start your installation by having no more than
4Gb of RAM and wait until this starts to be
utilised before implementing more.

As far as kernel parameters are concerned these
need to be changed as part of your oracle
installation pre-requisites. These should be
changed depending on how many instances you
plan on having.

Crash dumps... well most now get compressed
pretty well, and it is unlikely that you will
a problem with a 2Gb dump partition to cater
for it if required.

-Michael
Anyone for a Mutiny ?
Steven Sim Kok Leong
Honored Contributor

Re: SWAP Area Size & Kernel Parameters

Hi,

Take one example:

If you have two Oracle intances each using an SGA of 400 MB, then your shmmax of 1 GB should be a sufficient value.

If each of your Oracle server processes (assuming that you are not using MTS) takes up 20 MB of memory individually (apart from the shared pool in the SGA) and you are supporting 2000 concurrent Oracle server connections, i.e. 1200 * 5 MB = 6 GB, then 6 GB of memory will not be insufficient (especially when you factor in the SGA memory requirements).

If you can't immediately find any more memory but you need to support 1200 concurrent Oracle server connections urgently, you can increase your swap to tide you over. I would look at swap as a temporary yet emergency solution to insufficient memory at unexpected peak periods of usage.

If however, you need to consistently support 1200 concurrent Oracle server connections (not just during peak periods), then purchasing more memory would be a better solution.

Hope this helps. Regards.

Steven Sim Kok Leong
Email: steven@beepz.com. Homepage: https://www.beepz.com
Steven Sim Kok Leong
Honored Contributor

Re: SWAP Area Size & Kernel Parameters

Hi,

Forgot to change the figures in the description when changing them in the computation. Should be:

... takes up 5 MB of memory individually (apart from the shared pool in the SGA) and you are supporting 1200 concurrent Oracle server connections, i.e. 1200 * 5 MB = 6 GB ...

Hope this helps. Regards.

Steven Sim Kok Leong
Email: steven@beepz.com. Homepage: https://www.beepz.com
Shahbaz_1
Regular Advisor

Re: SWAP Area Size & Kernel Parameters

Thanks every body.
Regards
Syed
Let's share the great thing "THE KNOWLEDGE"