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The DELETE with the multiple NOT EXISTS went from running for 2 hours to delete 30,000 records, to deleting over 100,000 records in minutes. ." An Oracle ACE notes this script to rebuild his indexes.

"I eventually wrote a simple query that generates a list of candidates for index rebuilds, and the commands necessary to rebuild the indexes once the tables reached a point where it was necessary.

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Here, Robin Schumacher proves that an index that is rebuilt in a larger tablespace will contain more index entries be block, and have a flatter structure: In an Oracle World 2003 presentation titled: Oracle Database 10g: The Self-Managing Database by Sushil Kumar of Oracle Corporation, Kumar states that the new Automatic Maintenance Tasks (AMT) Oracle10g feature will "automatically detect and re-build sub-optimal indexes.

However, the 10g segment advisor only recommends index rebuilding from a space reclamation perspective, not for performance.

Here are the pros and cons of this highly emotional issue: So who is right? There is a huge body of evidence that index rebuilding makes the end-users report faster response time, and I have to wonder if this is only a Placebo Effect, with no scientific basis.

Some experts suspect a Placebo Effect may be at work here, and the end-users, knowing that they have new index trees, report a performance gain when none exists.

In an OLTP system, index space is often greater than the space allocated for tables, and fast row data access is critical for sub-second response time.

As we may know, Oracle offers a wealth of index structures: OPERATION----------------------------------------------------------------------OPTIONS OBJECT_NAME POSITION------------------------------ ---------------------------- ---------- SELECT STATEMENT 2 TABLE ACCESSBY INDEX ROWID EMP 1 BITMAP CONVERSIONTO ROWIDS 1 BITMAP AND BITMAP INDEXSINGLE VALUE DEPT_BIT 1 BITMAP INDEXSINGLE VALUE JOB_BIT 2 While the internals of Oracle indexing are very complex and open to debate, there are some things that you can do to explore the internal structures of your indexes. s take a closer look at the method that I use to reveal index structures.Some experts claim that periodic rebuilding of Oracle b-tree indexes greatly improves space usage and access speed, while other experts maintain that Oracle indexes should: rarely be rebuilt.Interestingly, Oracle reports that the new Oracle10g Automatic Maintenance Tasks (AMT) will automatically detect indexes that are in need of re-building.This Kim Floss article shows the Oracle 10g segment advisor recommending a rebuild of an index: 'The page lists all the segments (table, index, and so on) that constitute the object under review.The default view ("View Segments Recommended to Shrink") lists any segments that have free space you can reclaim.' There are many myths and legends surrounding the use of Oracle indexes, especially the ongoing passionate debate about rebuilding of indexes for improving performance.The query reads a table we built called TABLE_MODIFICATIONS that we loaded each night from DBA_TAB_MODIFICATIONS before we ran statistics.

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