Raj First, you may want to consider reading up on virtual memory vs. real memory. Most modern operating systems use virtual memory. Your program runs in the virtual memory address space. The O.S. decides which portion of the virtual memory address space to have in real memory at any given time. Second, Oracle isn't in charge of a computer's memory. That is the purpose of the operating system. Oracle can makes requests for the memory it requires. Ultimately how those requests are satisfied are up to the operating system. Suppose you had two Oracle instances or an Oracle and a Sybase database running on the same server. You can't allow each of those applications to decide what they will do to the underlying resources. You need a higher authority to decide who will get what resource, whether it is memory, CPU, or I/O. That higher authority is the O.S. Now, to how it actually works, I can only speak to my experience with Unix. Usually the SGA is kept in real memory. When you overcommit the real memory, the O.S. has to page portions of the SGA back in and out very rapidly. This can produce "thrashing". There are several Oracle parameters that can affect how the O.S. handles the SGA, like PRE_PAGE_SGA.
Dennis Williams DBA, 80%OCP, 100% DBA Lifetouch, Inc. [EMAIL PROTECTED] -----Original Message----- Sent: Friday, September 05, 2003 11:09 PM To: Multiple recipients of list ORACLE-L Dear Friends, Good Morning, Have just read(in some book) that Oracle allocates SGA in virtual memory of the server. My understanding is that Oracle first try to allocate in real memory because it is relatively faster for accessing. Please clarify, any case studies , scenarios would explain this well , I hope. Thanks a lot. Rajuveera ************************************************************************** This email (including any attachments) is intended for the sole use of the intended recipient/s and may contain material that is CONFIDENTIAL AND PRIVATE COMPANY INFORMATION. Any review or reliance by others or copying or distribution or forwarding of any or all of the contents in this message is STRICTLY PROHIBITED. If you are not the intended recipient, please contact the sender by email and delete all copies; your cooperation in this regard is appreciated. ************************************************************************** -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Veeraraju_Mareddi INET: [EMAIL PROTECTED] Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing). -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: DENNIS WILLIAMS INET: [EMAIL PROTECTED] Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
