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Oracle 8i SGA and memory

Lionel MAZE
Occasional Advisor

Oracle 8i SGA and memory


Is there something to lock the SGA in memory ? This can permit the SGA to stay in memory and can't be swap.

Any suggestions ?

Thank You.
Steven Gillard_2
Honored Contributor

Re: Oracle 8i SGA and memory

Yes, use the lock_sga init.ora parameter:

lock_sga = true

harry d brown jr
Honored Contributor

Re: Oracle 8i SGA and memory

One way, although it doesn't pin the SGA, it gives it more memory to the system overall, is by reducing dbc_max_pct to 10 (or less) and dbc_min_pct to 5.

live free or die
Live Free or Die
Trusted Contributor

Re: Oracle 8i SGA and memory

I concurr with Harry, after much tweaking setting those two value to 5% (I have 6 GB Memoery today) my SGA stayed put in most cases.
Anthony deRito
Respected Contributor

Re: Oracle 8i SGA and memory

Carefull when you lock memory. You may be taking away important memory resources for paging and deactiviation activities. Just to be sure, after you increase the lockable memory with your application run dmesg and check out the locakable memory amount as compared to the memory available just to make sure you don't run into memory resource problems.

Memory Information:
physical page size = 4096 bytes, logical page size = 4096 bytes
Physical: 2097152 Kbytes, lockable: 1650404 Kbytes, available: 1895808 Kbytes

You may need to also look at the unlockable_mem kernel parameter. This parameter will affect how much memory can be locked. If this value is set to zero, the size of unlockable memory is chosen at boot time.

Hope this helps.

Honored Contributor

Re: Oracle 8i SGA and memory

Just my personal option, i totally agree with Harry, i prefer increasing physical memory and pining busy objects. - this is my strategy.

hope this is helpful.

Honored Contributor

Re: Oracle 8i SGA and memory

Hello Lionel,

in addition to the init*ora parameter "lock_sga = true" I do prefer to use "pre_page_sga = true".
And in any case you NEED to set "/etc/provgroup" with a value like
dba: MLOCK
and NO empty lines in. Instead of "dba" you'll have to name your local Oracle-Admin group, of course.
Then you'll have to execute "/sbin/init.d/set_prgrp start".