Re: How much RAM is to much
- From: Gaja Krishna Vaidyanatha <gajav@xxxxxxxxx>
- To: andrew.kerber@xxxxxxxxx, RStorey@xxxxxxxxxxxxxxxxxx
- Date: Thu, 10 Feb 2011 11:48:20 -0800 (PST)
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.'
Other related posts:
