Re: How much RAM is to much
- From: Gaja Krishna Vaidyanatha <gajav@xxxxxxxxx>
- To: Andrew Kerber <andrew.kerber@xxxxxxxxx>
- Date: Thu, 10 Feb 2011 11:58:36 -0800 (PST)
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@xxxxxxxxx>
To: Gaja Krishna Vaidyanatha <gajav@xxxxxxxxx>
Cc: RStorey@xxxxxxxxxxxxxxxxxx; oracle-l-freelists <oracle-l@xxxxxxxxxxxxx>
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@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.'
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