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row movement in Oracle

Posted on 2010-01-08
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Last Modified: 2012-06-27
 Hello Experts !
   
   What is enable row movement in Oracle ?
    Where we can use this options in database ?
    What are the performance issues a DBA can face if it remains enabled on some frequently used  tables in database ?

Thnaks & regards
  JD
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Question by:junaid_baig1
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sdstuber earned 1000 total points
ID: 26210282
just as it sounds,  "row movement" means the row can be physically moved from one area to another as part of updates.  That is,  the data may be deleted from one data file and rewritten to another part of the datafile, or a new datafile, or even a new tablespace entirely in some cases.

Partitioning is probably the most common use of this feature.
For example,

I have data partitioned by year and each year-partition is in its own tablespace.

Now, I update a row that was for 2009 to be 2010.  It must go into a new partition, but the only way it can do that is if the table allows row movement because the update requires a physical rearrangement, not just twiddling some bytes.

Row movement is a performance drag when it happens but if it's necessary then it's necessary.

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by:sdstuber
ID: 26210298
if the data changes never require row movement then having it enabled won't incurr a performance penalty.
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by:Shaju Kumbalath
ID: 26210301
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by:sdstuber
ID: 26210337
if you enable row movement for the purposes of reorganization, as in the link above.  I suggest you enable, do the reorg and then disable.

But first, be sure the reorg is necessary.
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by:schwertner
schwertner earned 1000 total points
ID: 26210531
The positive sides of row movements are explained   by the previous postings and also here :
http://www.databasejournal.com/features/oracle/article.php/3676401/Row-Movement-in-Oracle.htm

But there are also negative movements called row migration. This means that there is not enough space in the Oracle Data Block (by update operation) for the record and Oracle has placed the record in otherOracle block. But this slows down the processing and should be avoided.

Sometimes Oracle blocks get fragmented on the disk device. In this case some techniques (export/import or tablespace change) can help to improve the placement.
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by:slightwv (䄆 Netminder)
ID: 26210614
These questions sound a lot like homework/exam questions.
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by:schwertner
ID: 26213110
@ slightwv:

Row Movement is not part even of Oracle University DBA Courses.
So (if you are right) this should be a very sophisticated course in a technological University

@ junaid_baig1: please clarify, because slightwv has the power to close the tread (I not :) )
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Author Closing Comment

by:junaid_baig1
ID: 31674551

 Thanks !!
 we faced this Issues as new Year begins!

@schwertner:  Thanks!! I think slightwv couldn't get point..
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Author Comment

by:junaid_baig1
ID: 26214214


 @slightwv:  i think you didn't get the point that i raised!  This is quite a common Issue that Development DBA team faced every now & than & They 've discussed the Issue with US  ! 'm DBA ADMIn !    

   
Thanks & regards
  JD
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