Yeah, these are the /proc/sys/vm/swappiness and /proc/sys/vm/overcommit* parameters. I think in a regular database server the swappiness should be 0 as background file maintenance operations (like backups, tar, gzip, find) should not be able to page out Oracle's server processes. And allowing virtual memory overcommit is even a bigger joke ( having /proc/sys/vm/overcommit_memory as 0 or 1 ). This allows Linux to commit more address space to process than there's swap+RAM available. Thus when the processes actually start touching the pages and really reserving them from swap/RAM then they can just die in the page fault code. Or even worse - the out of memory killer (OOM killer) will just pick a "random" process and kill it to free up some memory! The overcommit_memory parameter should be 2 in a database server, along sufficient swap space to back the memory allocations. -- Tanel Poder http://blog.tanelpoder.com On Wed, Jun 24, 2009 at 10:43 AM, Teehan, Mark < mark.teehan@xxxxxxxxxxxxxxxxx> wrote: > Hi Mudhlavan, > > I agree with LS, and much depends on your version of Redhat. > Linux does behave differently and uses any free RAM to speed up filesystem > operations; to prove it run a top while you gzip a file and see what happens > to free RAM. > Check orca if you have it running; you should see memory usage gradually > increase following a restart dependant on filesystem operations. > I've seen chronic problems with memory starvation on RH4; I believe it was > hardware dependant but if the OS allowed free RAM to drop too low (15MB or > so) during heavy I/O that is not using direct I/O, (gzips, ftp, hot > backups) then kswapd kicked in a little to late to rescue the situation and > could sometimes hang the OS. > I believe these problems are fixed on RH5. Performance problems are > probably not related to swap at all; and AWR is probably the best tool on > hand. > > Rgds > Mark > > > ------------------------------ > *From:* oracle-l-bounce@xxxxxxxxxxxxx [mailto: > oracle-l-bounce@xxxxxxxxxxxxx] *On Behalf Of *LS Cheng > *Sent:* 24 June 2009 14:44 > *To:* moovarkku.mudhalvan@xxxxxxxxxxxxxxxx > *Cc:* oracle-l@xxxxxxxxxxxxx > *Subject:* Re: Physical Memory Fully Used and Swap is Not Used > > Hi > > In the IO side you should enable direct i/o and aio in Linux (if you are > using filesystems). > > In the memory side you should enable hugepages, this is a nonswappable > memory, i.e all SGA will be in physical memory. Be careful when setting this > up though, some miss calculations will make Oracle use normal pages. > > Regarding Linux uses all memory, that behaviour is default behaviour for > ages, Linux tries to cache everything and uses all memory. Why leave memory > free when you can use it, I think that is philosophy. There were some kernel > parameters to change this behaviour but since Linux changes pretty fast and > I cant really tell you if they still work in your Linux platform. Last time > I checked they were working for RHEL 4 but no longer in RHEL 5 and I cant > find the corresponding kernel parameters in RHEL 5 :-( > > About your performance problem I think you better identify them first > inside database (look some statspack or AWR if you have license). If Swap is > not in use then the OS is not swapping, if there are heavy swap going on in > Linux kswapd kicks in, in heavy memory starvation system when kswapd wakes > up and freeing memory it hangs the system too! :-) > > > Thanks > > -- > LSC > > > > On Tue, Jun 23, 2009 at 7:41 AM, Mudhalvan Moovarkku < > moovarkku.mudhalvan@xxxxxxxxxxxxxxxx> wrote: > >> Dear DBAs, >> >> We have recently migrated Oracle from 8.0.6 on HP-Unix to >> 10.2.0.4 on Red Hat Linux >> >> Earlier the same application worked fine with 7GB RAM on HP-UNIX >> on PA-RISC >> >> Upgraded system on IBM X 3850 with 16GB RAM but still we have >> some performance issue. >> >> I knew there is some lagging because of Hardware Architecture but >> it is too bad 7 GB to 16GB RAM but still have performance. >> >> Please look at data collected from RDA. Looking at this scenario >> my physical memory is fullly used but Swap is not at all used. >> >> Total Physical Memory 16032 MiB >> >> Available Physical Memory 30 MiB >> >> Swap: Max Size 24575 MiB >> >> Swap: Available 24505 MiB >> >> Swap: In Use 70 MiB >> >> We know there is some performance issue in application. I would >> like to make as much as possible from Database/Linux side tunning to >> provide atlease peaceful performance. Can any body through some light on why >> the swap is not at all used. >> >> Regards >> >> Mudhalvan M.M >> >> > ============================================================================== > Please access the attached hyperlink for an important electronic > communications disclaimer: > http://www.credit-suisse.com/legal/en/disclaimer_email_ib.html > ============================================================================== > > -- Tanel Poder http://blog.tanelpoder.com