RE: SGA_MAX_SIZE on Solaris
- From: Michael Milligan <Michael.Milligan@xxxxxxxxxxx>
- To: "'oracle-l@xxxxxxxxxxxxx'" <oracle-l@xxxxxxxxxxxxx>
- Date: Thu, 11 Mar 2004 17:44:15 -0600
SGA_MAX_SIZE tells Oracle the maximum allowed memory allocation for the SGA.
You can dynamically alter the size of the SGA up to SGA_MAX_SIZE. Here's why
you want to set it: it has a default value. The default value of
SGA_MAX_SIZE is the value for sga size on startup - not too much. Typically
not a lot more than the shared_pool_size value on startup (maybe 20MB more).
Efictively, this leaves you no room to increase the size of the sga. So set
SGA_MAX_SIZE to a larghe value, like 256M, or whatever. It doesn't load any
more memory at start up, but allows you to increase up to this value.
-----Original Message-----
From: DENNIS WILLIAMS [mailto:DWILLIAMS@xxxxxxxxxxxxx]
Sent: Thursday, March 11, 2004 3:08 PM
To: 'oracle-l@xxxxxxxxxxxxx'
Subject: SGA_MAX_SIZE on Solaris
Has anyone experimented with SGA_MAX_SIZE? Does Oracle request that amount
of memory on startup? If memory of the components like SHARED_POOL_SIZE and
DB_CACHE_SIZE are smaller than SGA_MAX_SIZE, does Oracle only request enough
memory for the components? If the size of one of the components is reduced
dynamically, does Solaris eventually reclaim that space?
I have a test system with many Oracle9i instances. Most are little used,
and I allocate only a small amount of memory. However, now and then a
development group will start pounding an instance. Often they run out of
memory. So I have to audit the memory settings of all instances, then notify
developers on other instances that I need to bounce their instance to
retrieve some memory. A hassle for everyone concerned.
I'm wondering if I can set the SGA_MAX_SIZE high on all instances, but
then just allocate a small amount of memory. Then if an instance needs more
memory, I could allocate it dynamically, and also dynamically reduce the
memory allocated in other instances.
Any thoughts appreciated.
Dennis Williams
DBA
Lifetouch, Inc.
dwilliams@xxxxxxxxxxxxx
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