Why doesn't the Oracle optimizer use my index?
Querying too much data
Most Oracle developers know that an index is useful when you can use it to restrict your result set to a small number of the total rows in a table.
So, the obvious side…
Have you ever had to make fundamental changes to a table in Oracle, but haven't been able to get any downtime? I'm talking things like:
* Dropping columns
* Shrinking allocated space
* Removing chained blocks and restoring the PCTFREE