Memory allocation best practices

[blainepruitt]

Greetings all,

I'm not an Oracle DBA by practice so this question will come off as somewhat naive and will no doubt get varied responses from the DBA community.

I'm a Unix Systems Engineer for my company and I'm helping to isolate some performance issues on one of our test boxes before moving the environment into production. The box in question is running two database instances and has 4 GB of memory and plenty of other resources (CPU, disk space, etc.). The system's kernel.shmmax setting is configured to use all of the available RAM and at this point nothing appears to be swapping.

Now for me to finally get to my question: Would you consider this to be the best practice when tuning a database? Maybe I'm just a bit uneducated but it seems to me that you would want to cap the database around 2.5 - 3GB of RAM leaving the rest for the OS. All of the searches on the internet I have done thus far seems to show formulas for tuning, but before implementing them I wanted to get advice from the professionals.

Does this sound logical or am I just crazy? Thanks in advance for your responses.

-BP

 

[SantaMufasa]

nothing appears to be swapping.

...and that is one of the more important goals of tuning/sizing the SGA.


Frankly, I am not very scientific about sizing the components of the SGA (shared pool, buffer cache, and log buffer). For larger systems, I simply allocate 500MB for shared pool, the same for the buffer cache, and around 250K for the log buffer; and I've NEVER had an SGA problem under those circumstances.

But those that do it "scientifically", more power to 'em.

Mufasa
(aka Dave of Sandy, Utah, USA)
[I provide low-cost, remote Database Administration services: www.dasages.com]

 

[dbtoo2001]

Go with oracle recommendations and make adjustments from there.

http://download.oracle.com/docs/html/A96167_01/pre.htm#i1076781

Santa's reply is relative to initialization parameters for the database instance. If I interpret your question correctly, you are asking about kernel parameters. Assuming you are a licensed user... check metalink for kernel settings. You can also open a tar and ask for recommendations.

 

[blainepruitt]

dbtoo2001 you are correct, I'm looking for kernel parameters, although Mufasa's information is helpful as well as it helps give me a better understanding of tuning from top to bottom. I personally don't have a login for the site, but I can get the login information from one of our DBAs.

Thanks for both replies.