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Don Burleson Blog 







Scheduling table and index reorganizations?

Oracle Tips by Burleson Consulting

Many Oracle professionals schedule Oracle index and table rebuilds during downtime when their system is idle or use the dbms_redefinition utility to reorg a table during up-time.  However, some DBA "scientists" believe that no DBA task should be done without a "proof" of the benefit, in advance.  A complex task, true, but one that could be done with the help of historical SQL access data from the dba_hist_sql_plan table.


There is a great-deal of controversy about the benefits of rebuilding tables and indexes, and some say that indexes and tables "seldom" need re-building, a very dangerous "don't worry about it" approach IMHO.


I think that 10g has all the data needed to predict the reduction in LIO and PIO from a reorganization.  The reorganization of a table/index also gives you the opportunity to adjust the object structure so prevent a re-occurrence of the fragmentation issue.  It's well understood that adjusting how the table and index data are stored on the data blocks can have a positive impact on query response time.


In an OracleWorld 2003 presentation titled  ?Oracle Database 10g: The Self-Managing Database? by Sushil Kumar of Oracle Corporation, Kumar states that the Automatic Maintenance Tasks (AMT) Oracle10g feature will automatically detect and re-build sub-optimal indexes.


Also, see these notes on using multiple blocksizes in Oracle.

In fact, there was a great "peek" presentation at RMOUG that suggests that predictive modeling will be an important new feature in 11g.


If you like Oracle tuning, you might enjoy my book "Oracle Tuning: The Definitive Reference", with 950 pages of tuning tips and scripts. 

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.



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