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Rebuilding Unbalanced Indexes

Oracle Tips by Burleson Consulting

The Data Warehouse Development Life Cycle

Oracle Features for the Data Warehouse

Rebuilding the Unbalanced Indexes

So, what is the solution?  Oracle version 7.2 and above provides a facility that rebuilds an index in-place.  This is done by issuing an ALTER INDEX command:

ALTER INDEX xxx REBUILD TABLESPACE yyy;

WARNING:  You must specify the tablespace name when using this command.  If the tablespace name is not present, Oracle will attempt to rebuild the index in the default tablespace name of the connected user who is issuing the command.

Let’s take a look at what happens in an in-place rebuild of an Oracle index. The index will be rebuilt in-place with the same number of extents as the original index.  Hence, this command is not useful for reorganizing an index into a single extent.  Also, each index node will be rebuilt in-place and the excessive levels and deleted leaf rows will be fixed.  Since the goal of the data warehouse manager is to rebuild only those indexes that have more than three levels or lot’s of deleted leaf rows, we have the id5.sql script generate the rebuild commands directly from the temp_stat table and stored the output as id6.sql.

WARNING:  While Oracle does not publish how the rebuild command works internally, you must have extra space, equal to the index size, in each tablespace in order to issue the rebuild command.  If Oracle cannot get enough scratch space in the target tablespace, the existing index will remain intact, and you will receive the message FAILED TO ALLOCATE AN EXTENT OF SIZE xxx IN TABLESPACE yyy.


This is an excerpt from "High Performance Data Warehousing", copyright 1997.

If you like Oracle tuning, you may enjoy the book Oracle Tuning: The Definitive Reference , with over 900 pages of BC's favorite tuning tips & scripts. 

You can buy it directly from the publisher and save 30%, and get instant access to the code depot of Oracle tuning scripts.


 

     

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