| sga &redolog [message #59257] |
Thu, 06 November 2003 12:42  |
Jasmine
Messages: 23
Registered: December 2000
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Junior Member |
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hi
If we have to create an database around 50gb for normal transactions like 20 users for dataentryhow much space we have to allocate for sharedpool and size of redolog,rollback(undo).It not 24 * 7 database any methods to calculate the size
Thanks in advance
jasmine
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| Re: sga &redolog [message #59260 is a reply to message #59257] |
Thu, 06 November 2003 20:55  |
Daljit Singh
Messages: 290
Registered: October 2003
Location: Texas
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Senior Member |
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Hi,
If ur virtual memory is less than 1 GB then u can use this to calculate the size of SGA :
VM * .55 = Toal SGA out of which
VM * .45 = Shared Pool
VM * .45 = Buffer Pool
VM * .10 = LOG Buffer
If ur VM is greater than 1 GB then u can user 65 to 70 percent for the SGA.
It doesn't mean that it is a perfect formula which will get fit in every situation, but in initial I use this formula to calculate the SGA setup. and after that according to the performance and requirements the size can be increased/decreased.
I hope it will help u.
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| Re: sga &redolog [message #59272 is a reply to message #59260] |
Fri, 07 November 2003 09:34 |
Thiru
Messages: 1089
Registered: May 2002
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Senior Member |
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VM * .55 for SGA may be too much and could result in paging and swapping. Remember, VM = Physical memory + Swap space. Say your Physical memory is 1GB and Swap space is 2GB, so your total virtual memory = 1+2=3 GB .
And 0.55 * 3GB is around 1.5GB which is more than your Physical memory , resulting in a large portion of your SGA being paged out to swap bringing the database performance down heavily. Besides this means almost all of your Server processes with be swapped out to disk for lack of free memory and thats a big NO NO.
Try to size your SGA and memory for PGA based on your Physical memory. You dont want your SGA to be paged out or PGA to be swapped out. Some amount of Paging is acceptable though.
I try to make the total size of SGAs of all instances put together , not to exceed 60% of the Phyiscal memory, allocating space for Kernel memory and Server processes.
-Thiru
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| Re: sga &redolog [message #59286 is a reply to message #59272] |
Sun, 09 November 2003 23:09 |
Daljit Singh
Messages: 290
Registered: October 2003
Location: Texas
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Senior Member |
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Hi,
I agree with u Thiru, actually i was not calculating the swap space in VM. In my formula VM means only Physical Memory.
Thanx.
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| Re: sga &redolog [message #59292 is a reply to message #59286] |
Mon, 10 November 2003 07:28 |
Thiru
Messages: 1089
Registered: May 2002
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Senior Member |
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Ok,no problem. People might get confused when you refer to Virtual memory for SGA size calculations,although it does play a part,in that it sets the max addressable memory.
Maybe you could just call it as Physical Memory or RAM ?
-Thiru
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