RE: SGA_MAX_SIZE on Solaris
- From: "Rognes, Sten" <Sten.Rognes@xxxxxxxxxx>
- To: "'oracle-l@xxxxxxxxxxxxx'" <oracle-l@xxxxxxxxxxxxx>
- Date: Thu, 11 Mar 2004 17:09:12 -0700
Be careful with using sga_max_size on Solaris (I am assuming that's your
platform). There is a Solaris bug which is claimed to can cause up to a 90%
performance degradation, bug#4675878. This bug affects both Solaris 8 and
earlier releases of Solaris 9. Although there are a Solaris 8 patch
available or in the works for this, I would not recommend using this feature
unless you are on Solaris 9 update 2(4/03) where large page support is
introduced for DISM segments and DISM and ISM performance is similar.
There are some notes on Metalink that will answer your questions below,
check out # 151222.1.
Sten
-----Original Message-----
From: DENNIS WILLIAMS [mailto:DWILLIAMS@xxxxxxxxxxxxx]
Sent: Thursday, March 11, 2004 2:08 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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