Oracle db_block_checksum performance bug

We recently ran across a pretty strange performance bug with the checksum function of Oracle. This bug (6814520) causes excessive CPU to be used for the checksum routine. The checksum feature of Oracle is enabled by the db_block_checksum=TRUE parameter in Oracle. With the release of Oracle 10gR2, "TRUE" is the default setting. The order of magnitude of CPU overhead depends on the type of Solaris SPARC architecture.

Chip     %overhead
----     ---------
SPARC64       250%  
USIV           45%  
------------------
w/patch         8% 

Oracle released a patch via metalink to address this situation. This patch is for 10.2.0.3 installations. The fix will be included in: 11.1.0.7, 10.2.0.4, and 10.2.0.5.

If you are unsure whether or not you are hitting this bug, you can easily alter this parameter on the fly:
    SQL> alter system set db_block_checksum=FALSE
Warning, this will disable the checksum feature and blocks written when this is turned to FALSE will not contain checksum information.

Regardless of whether you are currently hitting the bug or not, the recommendation is:
    INSTALL "6814520" WHEN USING ORACLE 10.2.0.3 !!!
Comments:

Hi Glen,
Thanks for this useful piece of information. I have a new mission critical initiative that I am currently working on and it is based on 10.2.0.3. I am curious to know if Sun Engineering used DTRACE to find out what piece of code was cusing issue in Oracle kernel? Also, I am assuming that this bug is specific to S10?
Thanks

Posted by Amir Hameed on March 15, 2008 at 06:54 AM PDT #

Hello,

do you know if this bug hits 10.2.0.2 installations? I cannot find any information about it on metalink - maybe it's non-public.

Posted by Szymon on March 16, 2008 at 08:37 PM PDT #

Sorry for the delayed comment responses :)

AFAIK the checksum bug is present in all 10.2.x releases of Oracle... and you can see the impact using Dtrace. The "hotuser" script from the Dtrace toolkit was used to identify the hot Oracle functions - quite useful.

Posted by Glenn Fawcett on April 14, 2008 at 03:59 AM PDT #

ZFS does not support directIO, so I am not sure of the effects. I would check with StorNext for cvfs questions.

Regardless, I would install the patch since it is considered mandatory.

Posted by Glenn Fawcett on May 13, 2008 at 02:45 AM PDT #

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This blog discusses performance topics as running on Sun servers. The main focus is in database performance and architecture but other topics can and will creep in.

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