RE: Reducing sga_target in 10gR2 without getting ORA-00827

  • From: "Schultz, Charles" <sac@xxxxxxxxxxxxx>
  • To: <topshot.rhit@xxxxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
  • Date: Fri, 16 Jun 2006 09:54:08 -0500

We had significant problems with sga_target, enough that we finally
turned it off. Apparently, in 10.2.0.1 there are some issues with the
algorithm that allocates/deallocates memory which can cause degradation.

Our Support Analyst(s) referenced the following bugs:
4466399/4472338 (dup) (SR 5386579.993): SYSTEM WIDE HANG ON MMON WAITING
FOR 'SGA ALLOCATION FORCING COMPONENT GROWTH':
4507532 (SR 5256243.992): SGA_TARGET DOESN'T WORK AS EXPECTED

Not sure if this is relevant for your situation, but wanted to offer it
up just in case.

-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Michael Ray
Sent: Friday, June 16, 2006 9:31 AM
To: oracle-l@xxxxxxxxxxxxx
Subject: Reducing sga_target in 10gR2 without getting ORA-00827

To attempt to mitigate ORA-04030 crashes we've been experiencing, Oracle
has suggested lowering sga_target. Unfortunately, the log/trace files
have provided no clues at all as to what is causing this crash every 3-5
weeks. The server has 4GB of physical RAM, but is not using the /3GB
switch so Oracle can only access 2GB. Currently sga_target is set at
1.2GB. The server runs only this 1 instance of Oracle so Windows has
plenty of mem.

select * from v$sga_dynamic_free_memory gives 0 because
sga_target=sga_max_size so Oracle has no memory to grow if needed. It
shouldn't need to since 1.2GB should be way more mem than it needs for
SGA.

Based on note 295626.1 I don't think I can reduce sga_target appreciably
without getting ORA-00827 (could not shrink sga_target to specified
value). Currently the sum of the min sizes

(select component, current_size/1024/1024 "CURRENT_SIZE",
        min_size/1024/1024 "MIN_SIZE",
        user_specified_size/1024/1024 "USER_SPECIFIED_SIZE"
from v$sga_dynamic_components)

is 1188 and sga_target is 1200.

Is there any way I can reduce sga_target to 1000 dynamically? Will I
just have to keep doing it in small steps of 12 for example?

-- 

Sincerely,
Michael Ray
Topshot Systems LLC
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