Re: sga_max_size - pre-allocated at instance startup?

From: Mladen Gogala <gogala_at_sbcglobal.net>
Date: Fri, 03 Mar 2006 13:53:49 GMT
Message-Id: <pan.2006.03.03.13.53.46.792783@sbcglobal.net>

On Thu, 02 Mar 2006 09:37:24 -0800, deebeeay_at_gmail.com wrote:

> Hi Guys,
>
> Is sga_max_size pre-allocated in memory at instance startup?

Let's check:
SQL> show parameter sga

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
lock_sga                             boolean     FALSE
pre_page_sga                         boolean     FALSE
sga_max_size                         big integer 320M
sga_target                           big integer 256M

SQL>
[root_at_medo ~]# ipcs -m|grep oracle;bc
0xa582a75c 589838 oracle 640 339738624 23 bc 1.06
Copyright 1991-1994, 1997, 1998, 2000 Free Software Foundation, Inc. This is free software with ABSOLUTELY NO WARRANTY. For details type `warranty'.
339738624/1048576
324

$ uname -a
Linux medo.noip.com 2.6.15.4 #1 Tue Feb 21 20:34:25 EST 2006 i686 athlon i386 GNU/Linux $

As oracle uses the same POSIX IPC services across the whole range of Unix-like platforms, one can safely conclude that oracle will allocate all of the shared memory specified in the SGA_MAX_SIZE at the instance startup.

>
> I can't seem to find a definitive answer from docs or the web. Some
> suggest yes but only on certain OSs.

The definitive anser is "maybe".

-- 
http://www.mgogala.com

Received on Fri Mar 03 2006 - 07:53:49 CST