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SGA Sizing [message #322266]

Thu, 22 May 2008 23:33

hexmanju
Messages: 78
Registered: September 2005
Location: MUMBAI

Member

Hi

Long time doubt ?

In Oracle Database when we specify the SGA size thru(SGA_MAX_SIZE) or SGA_TARGET(10g)equal to 8GB and say we have
physical memory of 4GB does it throw out of memory error.Say if i have allocated Virtual memory in addition to physical memory of 8GB more,will it be making use of that for the memory deficiency

How does Oracle Handle memory utilisation?

Thanks
MM

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Re: SGA Sizing [message #322267 is a reply to message #322266]

Thu, 22 May 2008 23:36

BlackSwan
Messages: 26766
Registered: January 2009
Location: SoCal

Senior Member

>How does Oracle Handle memory utilisation?
Oracle handles it well.

Why are you fixated on memory utilization?

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Re: SGA Sizing [message #322289 is a reply to message #322266]

Fri, 23 May 2008 00:28

abs_amit
Messages: 59
Registered: January 2006
Location: delhi

Member

first of All please explain
why you want SGA size 8GB?
what is the database size?
which operating system you are using ? (32bit or 64bit)

Regards
Amit Yadav

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Re: SGA Sizing [message #322771 is a reply to message #322289]

Mon, 26 May 2008 03:43

hexmanju
Messages: 78
Registered: September 2005
Location: MUMBAI

Member

I am just interested to know if Entire SGA fits in RAM..So i wanted to make it 8GB .My OS is 32-bit Micrsoft Windows.

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Re: SGA Sizing [message #322788 is a reply to message #322266]

Mon, 26 May 2008 04:24

varu123
Messages: 754
Registered: October 2007

Senior Member

Quote:

I am just interested to know if Entire SGA fits in RAM.

Entire SGA has to be fit in RAM.

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Re: SGA Sizing [message #322817 is a reply to message #322788]

Mon, 26 May 2008 05:41

abs_amit
Messages: 59
Registered: January 2006
Location: delhi

Member

It makes use of free (RAM + virtual/paging memory) while starting the instance

But its always better to let total SGA to be fit in RAM only.
Also remember that 100% RAM is not for the SGA only and also consider other processes which consume the RAM.

Windows OS requires 20% of RAM to work
Unix OS requires 10% of RAM.

So total RAM which can be allocated to SGA in windows OS is 80% and unix Os is 90%

We should also leave some RAM for individual oracle connections.
each oracle connection will use two megabytes of RAM plus (sort_area_size plus hash_area_size (or pga_aggregate_target)).

But the better practice is:

SGA size should not be more than 50% of RAM.

2GB SGA size should be sufficient for high transaction and big database. Still you can generate statistics later and tune it.

can also refer the below link for more details:
"http://www.dba-oracle.com/art_dbazine_ram.htm"

Regards
Amit Yadav

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Re: SGA Sizing [message #323792 is a reply to message #322817]

Thu, 29 May 2008 08:33

hexmanju
Messages: 78
Registered: September 2005
Location: MUMBAI

Member

Thanks for this Reply..It helps.

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