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Home -> Community -> Mailing Lists -> Oracle-L -> RE: SGA_MAX_SIZE on Solaris
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_at_LIFETOUCH.COM]
Sent: Thursday, March 11, 2004 2:08 PM
To: 'oracle-l_at_freelists.org'
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_at_lifetouch.com
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