Re: How much RAM is to much

Andrew,

There is nothing "off the wall" about what I said. Everyone SHOULD be using 
direct I/O but you will be surprised how many we encounter that still don't. You 
are correct in your assertion that if the database is configured with ASM, that 
direct I/O is automatically configured. But not everyone uses ASM. It is not a 
question of whether someone deliberately tries to use buffered I/O, but the 
issue of someone not configuring direct I/O in a database environment where ASM 
is not the storage persistence technology.

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: Gaja Krishna Vaidyanatha <gajav_at_yahoo.com>
Cc: RStorey_at_dcso.nashville.org; oracle-l-freelists <oracle-l_at_freelists.org>
Sent: Thu, February 10, 2011 11:54:22 AM
Subject: Re: How much RAM is to much

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-l