Chris, first of all - move to HugePages, because of much smaller PageTables and to avoid performance penalty by addressing such large memory second - don't allocate 80% of Linux memory to Oracle, because the rest needed not only for 'system memory', but for PageTables/Cache/processes(including Oracle) private structures like call stack, local variables e.t.c additionally - you don't have full control over PGA size - it's only recommended value, so oracle may overuse it if more memory needed. PS: Recently I have seen situation where 40% of 96GB RAM was dedicated to Oracle instance, and just after 15 minutes of running the application(with about of 1500 connected users) HUGE SWAPPING was started - the reason was bad SQL plans with high PGA demand -- Best Regards, Oleksandr Denysenko 28.01.2013 21:27, Christopher.Taylor2@xxxxxxxxxxxx ïèøåò: > > 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@xxxxxxxxx] > *Sent:* Monday, January 28, 2013 1:25 PM > *To:* Taylor Christopher - Nashville > *Cc:* oracle-l@xxxxxxxxxxxxx > *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 ïîëüçîâàòåëü <Christopher.Taylor2@xxxxxxxxxxxx > <mailto:Christopher.Taylor2@xxxxxxxxxxxx>> íàïèñàë: > > 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 > > > -- > //www.freelists.org/webpage/oracle-l > > > > > -- > Niall Litchfield > Oracle DBA > http://www.orawin.info > > -- > //www.freelists.org/webpage/oracle-l > > > -- > //www.freelists.org/webpage/oracle-l > -- //www.freelists.org/webpage/oracle-l