Re: How much RAM is to much
Date: Thu, 10 Feb 2011 13:54:22 -0600
Message-ID: <AANLkTinQC+k+4hgDQ=Ew=VdQWHiRc0bP=zw_oZJ2LTQc_at_mail.gmail.com>
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_at_yahoo.com>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_at_gmail.com>
> *To:* RStorey_at_dcso.nashville.org
> *Cc:* oracle-l-freelists <oracle-l_at_freelists.org>
> *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_at_dcso.nashville.org> 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.' -- http://www.freelists.org/webpage/oracle-lReceived on Thu Feb 10 2011 - 13:54:22 CST