Re: SGA, Oracle and RAM

Usually,

   you don't start from the RAM available on the server to decide how much SGA to allocate to Oracle. You should go the other way: make an estimate of how much Oracle will need, and see if your machine can handle it (if it can't, you'll need to purchase more RAM for your server). Leave some RAM on the server for the other applications and OS on the server. If the server has a RAM shortage, swapping of memory will kick in, and that can be a killer on Oracle (and the OS) performance.

Daniel

dbuckingham <member8912_at_dbforums.com> wrote in message news:<2900033.1053413639_at_dbforums.com>...
> 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.
Received on Tue May 20 2003 - 09:32:29 CDT