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Home -> Community -> Mailing Lists -> Oracle-L -> RE: SGA Question
There is a big problem with this it's called pre-emptive swapping and is yet
another wonderful feature of NT.
Basically as I understand it, Windows uses the whole of the defined virtual memory (including the swap file) and does some strange calculation to move things out of the physical into the virtual memory area, therefore swapping to disk some of your physical memory. This does not necessarily occur only when you have used up the amount of physical memory available to you, NT tries to guess what is likely to need memory and frees up physical memory for this. A rumour that I heard last year was that this pre-emptive swapping was VERY biased towards Microsoft tools and products and very unfriendly towards Oracle databases and applications.
To try and make sure that you keep the SGA in physical memory you must as with all O/S's not make it too big so that it can't fit in the physical memory available. With Oracle 8 you can also use the init.or parameter PRE_PAGE_SGA to try and keep the SGA in memory as much as possible.
To try and monitor this you must look at the number of 'hard faults' that occur. These are where memory requests are made to disc as opposed to 'soft faults' where requests are found elsewhere in the physical memory.
Use the performance monitor tool and track the Memory: page faults /sec and Memory:: pages input / sec. If the number of pages in are the same as the number of page faults then you are using 100% of swapped memory. You can also use the Memory : page reads /sec if this is above 5 per sec then you probably have a problem.
I have tried many ways to resolve the pre-emptive swapping characteristics of NT but have so far not succeeded. What I do make sure is that the number of process running on my servers are minimal (it is for Oracle and only Oracle) and also made sure that the total SGA size is no more than 50% of the available physical memory on each box.
Hope this helps
Stuart
-----Original Message-----
From: shailesh y [mailto:dba_account_at_yahoo.com]
Sent: 11 May 2000 07:28
To: Multiple recipients of list ORACLE-L
Subject: SGA Question
I do not know whether this has been discussed before. Is there anyway that i can find out whether the whole of SGA is in real memory or if not then how much is being swaped to disk so that the sizing may be corrected. I have Oracle (7.3 & 8) databases on NT servers with 128M - 1G of RAM.
TIA shailesh
-- Author: shailesh y INET: dba_account_at_yahoo.com Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051 San Diego, California -- Public Internet access / Mailing Lists -------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru_at_fatcity.com (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). ********************************************************************** This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify the system manager. This footnote also confirms that this email message has been swept by MIMEsweeper for the presence of computer viruses. www.mimesweeper.comReceived on Mon May 15 2000 - 04:22:40 CDT
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