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Home -> Community -> Mailing Lists -> Oracle-L -> RE: _row_cr setting in RAC
Amir, In Oracle9i Release 2, the Row CR feature can
partially alleviate the overhead of the global block
cleanout/rollback problem. The Row CR feature will
reduce the number of CR rollbacks and avoid a costly
block cleanout/rollback in a RAC environment. Instead
of performing a block cleanout, Row CR will only
attempt to generate a CR version for the particular
row. Currently, Row CR works for UPDATE statements
that have a Unique Index Scan or Fetch by Row ID in
the row source. Whenever there is a Fetch by Unique
Index row source in the execution plan, that causes CR
cleanout / rollback, Row CR will kick in. The
statistic Row CR attempts essentially measures the
number of updates that have this property that cause
CR cleanout or rollbacks to happen. The statistic Row
CR hits measures the success ratio of Row CR among the
attempts made. Oracle10g and beyond this feature
should extend for index range scans, as well as
further optimize cleanout processing.
To extend Row CR functionality, the hidden parameter _row_cr needs to be set to TRUE (default is FALSE). Row CR will be tried before invoking CR Rollback. The parameter can be changed dynamically, by using ALTER SYSTEM. Currently, Row CR is turned on only for Updates whose plan is Unique Scans or Fetch by Row ID. No other operation gets Row CR. When setting the _row_cr parameter to TRUE, Row CR will be attempted for ALL SQL (this will include Updates, Selects, Deletes and Joins) that have a Fetch By Unique Index OR a Fetch BY Row ID row source in the row source tree.
This parameter has benefited several bugs, however this is unsupported functionality. Consider setting _row_cr=TRUE if majority are immediate CR cleanouts
Scott
> We are demanding a reason and are not going to set
> it because it will
> not resolve our issue. I only wanted to know if
> anyone was using it.
>
> -----Original Message-----
> From: Wittenmyer Joel - CO
> [mailto:WITTENMYERJ_at_tusc.com]
> Sent: Monday, March 13, 2006 9:52 AM
> To: Hameed, Amir; oracle-l_at_freelists.org;
> racdba-bounce_at_freelists.org
> Subject: RE: _row_cr setting in RAC
>
> It's your environment. Demand a reason for the
> change before making it.
>
> -----Original Message-----
> From: oracle-l-bounce_at_freelists.org
> [mailto:oracle-l-bounce_at_freelists.org]
> On Behalf Of Hameed, Amir
> Sent: Friday, March 10, 2006 6:20 PM
> To: oracle-l_at_freelists.org;
> racdba-bounce_at_freelists.org
> Subject: _row_cr setting in RAC
>
> Folks,
> Is there anyone using this setting (_row_cr) with
> their 9i2 (9.2.0.6)
> RAC environment? Could someone please shed some
> light on under what
> circumstances this setting can help. We have a
> performance TAR opened
> with Oracle and the analyst is suggesting that
> setting this parameter
> would help. He did not give any reason for setting
> it though.
> Any help would be appreciated.
>
> Thanks
> Amir
>
> --
> http://www.freelists.org/webpage/oracle-l
>
> --
> http://www.freelists.org/webpage/oracle-l
>
>
>
-- http://www.freelists.org/webpage/oracle-lReceived on Mon Mar 13 2006 - 10:29:39 CST
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