BC remote Oracle DBA - Call (800) 766-1884  
Oracle Consulting Oracle Training Development

Remote DBA

Remote DBA Plans  

Remote DBA Service

Remote DBA RAC

Remote DBA Oracle Home
Remote DBA Oracle Training
Remote DBA SQL Tuning Consulting
Remote DBA Oracle Tuning Consulting
Remote DBA Data Warehouse Consulting
Remote DBA Oracle Project Management
Remote DBA Oracle Security Assessment
Remote DBA Unix Consulting
Burleson Books
Burleson Articles
Burleson Web Courses
Burleson Qualifications
Oracle Links
Remote DBA Oracle Monitoring
Remote DBA Support Benefits
Remote DBA Plans & Prices
Our Automation Strategy
What We Monitor
Oracle Apps Support
Print Our Brochure
Contact Us (e-mail)
Oracle Job Opportunities
Oracle Consulting Prices





Remote DBA services

Remote DBA Support

Remote DBA RAC

Remote DBA Reasons

Remote Oracle Tuning

Remote DBA Links

Oracle DBA Support

Oracle DBA Forum

Oracle Disaster

Oracle Training

Oracle Tuning

Oracle Training

 Remote DBA SQL Server

Remote MSSQL Consulting

Oracle DBA Hosting

Oracle License Negotiation








Oracle index maintenance

Oracle Tips by Burleson Consulting

Oracle Indexes Is Maintenance Required?

The question about whether Oracle indexes are self-balancing is largely a matter of semantics.  As rows are added to an empty table, Oracle controls the addition of same level blocks, called splitting, until the higher level index node is unable to hold any more key pointer pairs.  When the index can no longer split because the owner block is full, Oracle will spawn a whole new index level, keeping the index tree in perfect logical and physical balance.


However, DELETEs are a different story.  Physically, Oracle indexes are always balanced because empty blocks stay inside the tree structure after a massive DELETE.  Logically, Oracle indexes are not self-balancing because Oracle does not remove the dead blocks as they become empty.  For example, Figure 15.10 shows an Oracle index before a massive delete.


Figure 15.10:  A physical index before a massive row delete


Now, after a massive delete, the physical representation of the index is exactly the same because the empty data blocks remain as illustrated in Figure 15.11.  However, the logical internal pointer structure is quite unbalanced, because Oracle has routed around the deleted leaf nodes and has placed the empty index blocks back on the freelist, where they can be reused anywhere in the index tree structure


Figure 15.11:  The logical pointer structure of an index after a massive row delete


This type of sparse index is typical of an index on highly active tables with large scale INSERTs, DELETEs and UPDATEs.  There may be thousands of empty or near empty index blocks, and the sparse data can cause excessive I/O.  There are several types of Oracle execution steps that will run longer on this type of sparse index:

       Index Range Scans: Index range scans that must access many near empty blocks will have excessive I/O compared to a rebuilt index.

       Index Fast Full Scans: Because 70% of an index can be deleted and the index will still have the same number of data blocks, a full index scan might run many times slower before it is rebuilt.

Since the SQL must visit the sparse blocks, the task will take longer to execute.


This is an excerpt from my latest book "Oracle Tuning: The Definitive Reference". 

You can buy it direct from the publisher for 50%-off and get instant access to the code depot of Oracle tuning scripts:



Expert Remote DBA

BC is America's oldest and largest Remote DBA Oracle support provider.  Get real Remote DBA experts, call
BC Remote DBA today.



Remote DBA Service

Oracle Tuning Book


Advance SQL Tuning Book 

BC Oracle support

Oracle books by Rampant

Oracle monitoring software







BC Remote Oracle Support

Remote DBA

Remote DBA Services

Copyright 1996 -  2013 by Burleson. All rights reserved.

Oracle is the registered trademark of Oracle Corporation.

Hit Counter