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Oracle function based indexes


Oracle Tips by Burleson Consulting
 

One of the most important Oracle Silver Bullets is the function-based index.  A function-based index allows you to match any WHERE clause in an SQL statement and remove unnecessary large-table full-table scans with super-fast index range scans.

Here are the steps for tuning SQL with function-based indexes.

From the Oracle10g documentation we see a method for computing histograms on function-based indexes:

You should gather new column statistics on a table after creating a function-based index, to allow Oracle to collect column statistics equivalent information for the expression. This is done by calling the statistics-gathering procedure with the METHOD_OPT argument set to FOR ALL HIDDEN COLUMNS.

Note:  Once an FBI is created, you need to create CBO statistics, but beware that there are numerous bugs and issues when analyzing a function-based index.  See these important notes on statistics and function-based indexes.

I also discuss function-based indexes in my new book "Oracle Silver Bullets", and show how single acts (like building a function-based index) can have a positive effect on your entire Oracle database.  I've got a lot of great Oracle tuning tips and an online code depot with working examples of function-based indexes:

Also, see these related notes on Function-based indexes:

 

 

 

 
  
 

 
 
 
 
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Note: This Oracle documentation was created as a support and Oracle training reference for use by our DBA performance tuning consulting professionals.  Feel free to ask questions on our Oracle forum.

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