RE: SWAP Space Confusion Note 1354525.1

From: <Christopher.Taylor2_at_parallon.net>
Date: Mon, 28 Jan 2013 13:27:53 -0600
Message-ID: <F05D8DF1FB25F44085DB74CB916678E8856C52FD4E_at_NADCWPMSGCMS10.hca.corpad.net>

Well, you never really want any part of your Oracle instance memory sitting in swap. That's bad [from a performance perspective]. Typically you assign about 80% of Linux memory to Oracle if it's a dedicated Oracle server. (leaving 20% for system memory)

*However* I did just think about needing additional space for the page tables since we're using 4K pages right now.

I'll have to take that into account and deduct it from the 128 - that's about 10GB off the top right there just in page tables (to be on the safe side)

Chris

From: Oleksandr Denysenko [mailto:odenysenko_at_gmail.com] Sent: Monday, January 28, 2013 1:25 PM
To: Taylor Christopher - Nashville
Cc: oracle-l_at_freelists.org
Subject: RE: SWAP Space Confusion Note 1354525.1

Chris,

Don't allocate 120GB of 128 GB of available memory to oracle instance or you are just asking for troubles...

PS:
I have bad experience of allocating 8GB to SWAP from 32GB of available memory on HP-UX 11.23, but I think that on Linux you may use 16GB if you are not overallocating you memory

PS:
Just a question - are disks for swap more expensive than RAM ? :-)

Oleksandr Denysenko
28.01.2013 20:51 ÐÏÌØÚÏ×ÁÔÅÌØ <Christopher.Taylor2_at_parallon.net<mailto:Christopher.Taylor2_at_parallon.net>> ÎÁÐÉÓÁÌ: So, going back to this...
(env 10.2.0.4 RAC on 3 node RHEL 5.6 64-bit)

On a system with 128GB RAM, 100GB SGA, 20 GB PGA, 500 connected sessions (20-30 active), how confident can we be that 16GB of SWAP is sufficient? (side note: RHEL is running at mostly default settings such as vm.swappiness = 60)

I've seen notes all over the place on this and I'm wary setting the swap space too low but also don't want to set aside a large swap area just to have it sitting there doing mostly nothing.

Chris

Ref: 10gR2 SWAP Space Requirement For Systems Having Huge RAM [ID 1354525.1]

Per the above doc, the "GOAL" section says: "For Systems having Huge Memory (RAM) is it really required to have SWAP Space as 0.75 X RAM"

Per the Solution it says:
Solution
As per the Documentation below is the swap space requirement for 10gR2:

RAM                           Swap Space
===                           =========Up to 512 MB                  2 times the size of RAM

Between 1024 MB and 2048 MB 1.5 times the size of RAM Between 2049 MB and 8192 MB Equal to the size of RAM More than 8192 MB 0.75 times the size of RAM

As part of Unpublished Documentation Bug below are the new values for SWAP Space requirements approved by Oracle Development Team and also updated in 11.1 and 11.2 Install guides as below:

RAM                       Swap Space
===                       =========Between 1 GB and 2 GB     1.5 times the size of RAM
Between 2 GB and 16 GB    Equal to the size of RAM
More than 16 GB           16 GB

All the other pre-requisites mentioned for Oracle Database Software in the installation guide published by Oracle Development Team need to be completed as appropriate.

You may proceed with the swap space requirements as mentioned in the updated guides and ignore any swap related warnings during the installation of 10gR2.

Chris Taylor
Oracle DBA
Parallon IT&S

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Niall Litchfield
Oracle DBA
http://www.orawin.info

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http://www.freelists.org/webpage/oracle-l Received on Mon Jan 28 2013 - 20:27:53 CET