Problem:
I heard that 5.0 maintains indexes automatically.   Is it still necessary to 
deactivate and reactivate the indexes or backup and restore 
the database to rebalance indexes?

Solution:
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Note: The information in this article applies to
            InterBase versions 3.3 and up.
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The database does do garbage collection on indexes. This
prevents major imbalances from ocurring in indexes. However,
it is recommended that users still backup and restore their
databases anyway.