Re: SGA, Oracle and RAM

dbuckingham wrote:

> I am interested to know how Oracle uses the physical memory on a
> machine.
>
> When you size the parameters in the INIT.ORA file you determine the size
> of the SGA, but how much of this SGA is loaded into physical memory and
> how much is used by Virtual memory? (or is it more of a case, if the RAM
> is available, then it will grab it?)
>
> However, is this all of the RAM then that the instance needs? or will
> processes spawned by the Instance result in the Oracle DBMS using
> additional RAM as well (additional to that which it will grab upon
> booting the server)?
>
> I am asking this for I am about to build an Oracle server that will
> have multiple instances on it. But I am not sure exactly how big to
> make the SGA's do I create them to utilise the max amount of ram
> possible, or make them smaller so that there is a fair bit of ram left
> vacant on the machine?
>
> Can someone point me in the right direction, I have tried looking at
> various documentation out there, but it basically talks about sizing the
> various parameters to create the SGA. I have not found anything
> discussing my other thoughts.
>
> --
> Posted via http://dbforums.com

AFAIK Oracle's recommendation is that you not use more than 1/3 of the RAM on a machine.

Why are you building multiple instances on a single machine? Why not multiple schemas in a single instance each with its own tablespaces? What is the business case for the direction you have taken?

--
Daniel Morgan
http://www.outreach.washington.edu/extinfo/certprog/oad/oad_crs.asp
damorgan_at_x.washington.edu
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