Re: Oracle and Memory

On 17 Aug 96 01:06:20 -0700, richu_at_msn.com (Richard Hu) wrote:

>>This might sound like a totally idiotic question, since it
>>flys in the face of reason. But, an associate of mine just
>>came back from a Oracle class where the statement was made that
>>'having too much memory can cause problems with Oracle'. I
>>thought that this was totally absurd and the person in the
>>class didn't ask the obvious question, why?
 

>>Does this make sense to anyone or was the instructor out to lunch?
 

>>Thanks,
>>Joe
>
>
>More memory=ORACLE heaven...I cant see how more memory could ever
>really hurt. AT best you can have a large mahority of your database
>in RAM...this would not HURT at all and be lightning fast

Perhaps what they meant was that "allocating too much memory to Oracle can cause problems".

As a rule of thumb, don't ever allocate over 1/2 of the real ram on a machine to Oracle. Don't forget, we use dynamic memory as well as SGA memory. If you give it all to the SGA upon start up, you will be in paging heaven at runtime.

Also, having too many block buffers can harm performance. If my entire database was cached, it would HURT and could be painfully slow. Data on disk is easyly addressable (eg: rowid = file/block/row on block). Data in memory is a little less organized (read: sequentially searched). We can spend quite a bit of time (elaps and cpu time) searching RAM for something that may or may not be there OR we can do 1 or 2 io's and just get it. In many cases, doing the io's will be faster.

In order to support very large memory databases, you have to go about memory organization a little differently. Oracle with the VLM (Very Large Memory) option on 64 bit machines for example can handle gigabytes of information.

Thomas Kyte
Oracle Government
tkyte_at_us.oracle.com                          

http://govt.us.oracle.com -- Check out our web site! Brand new, uses Oracle Web Server and Database

statements and opinions are mine and do not necessarily reflect the opinions of Oracle Corporation Received on Mon Aug 19 1996 - 00:00:00 CEST