That's a rather off the wall comment Everyone uses direct IO, its standard for Oracle these days. I suppose some people may disable it if they are using a file system (I rather doubt), but am not even sure you can configure ASM to not use it. I cant imagine why anyone would try, for that matter. On Thu, Feb 10, 2011 at 1:48 PM, Gaja Krishna Vaidyanatha <gajav@xxxxxxxxx>wrote: > Andrew et. al, > > The percentage depends on whether or not direct I/O is configured and is > working per specification. If you have direct I/O properly configured, in > the big picture, the consumption of memory by the filesystem buffer cache > will not affect your memory consumption numbers. But if you do NOT have > direct I/O configured and depending on your operating system (Linux vs. > Unix), the issue then is what are the ceilings setup for the filesystem > buffer cache's memory consumption. The last time I checked there is no > equivalent of "bufhwm" (Solaris) or file_cache_max_pct (HP-UX) on Linux. > Which means that if you don't have direct I/O configured on Linux (which btw > is not good practice), you can be pretty much guaranteed that up to 100% of > configured memory can be utilized by the OS for the filesystem buffer cache. > There have been many customer cases in the past few years, where the lack of > direct I/O has caused significant paging/swapping overhead. The lack of > direct I/O will also increase "sys" CPU utilization and causing unnecessary > overhead and contention on the system. Not at all worth it! > > Bottom line - please enable direct I/O, make sure it is working (by > performing the relevant truss, strace etc) and then finalize the memory > allocations for your SGAs & PGAs. > > Cheers, > > Gaja > > Gaja Krishna Vaidyanatha, > Founder/Principal, DBPerfMan LLC > http://www.dbperfman.com > Phone - 001-(650)-743-6060 > Co-author:Oracle Insights:Tales of the Oak Table - > http://www.apress.com/book/bookDisplay.html?bID=314 > Co-author:Oracle Performance Tuning 101 - > http://www.amazon.com/gp/reader/0072131454/ref=sib_dp_pt/102-6130796-4625766 > > > ------------------------------ > *From:* Andrew Kerber <andrew.kerber@xxxxxxxxx> > *To:* RStorey@xxxxxxxxxxxxxxxxxx > *Cc:* oracle-l-freelists <oracle-l@xxxxxxxxxxxxx> > *Sent:* Thu, February 10, 2011 11:18:28 AM > *Subject:* Re: How much RAM is to much > > I generally use the rule of thumb for Linux/unix of oracle can have up to > 80% of the RAM on the system on a dedicated server. However, make sure > everything on the OS is configured per the installation instructions for > oracle before you start dedicating all those resources to oracle. > > On Thu, Feb 10, 2011 at 1:02 PM, Storey, Robert (DCSO) < > RStorey@xxxxxxxxxxxxxxxxxx> wrote: > >> So, I’m moving my 9i 32 bit database to a 10g 64 bit database. My 9i box >> has 4 gig of ram and the usual 23bit limitations. My SGA and such on the 9i >> box probably hovers around 1.2gig. >> >> >> >> I have 24 gig of ram on the new box. From a data aspect, that will darn >> near load my entire database to memory. >> >> >> >> So, in setting SGA_TARGET, how much is too much? Before I was told the >> box specs, I was thinking 3 gig. But, with 24 gig available, and I’m the >> ONLY application on the box….how much is to much? >> >> >> >> What are the benefits and cons to setting this value at say, 12gig, with a >> SGA_MAX value of 15G. >> >> >> >> >> > > > > -- > Andrew W. Kerber > > 'If at first you dont succeed, dont take up skydiving.' > -- Andrew W. Kerber 'If at first you dont succeed, dont take up skydiving.'