Oracle performance increased as a result of these reorganization operations, but this
improvement was not due to a decrease in the number of extents. When a table is
dropped and re-created, several things happened that increased performance:
??? Each block was loaded as full of rows as possible.
??? As a consequence, the high-water mark of the table (the highest block that has
ever had data in it) was set to its lowest point.
Backup and Recovery | 133
??? All indexes on the table were rebuilt, which meant that the index blocks were as
full as possible. The depth of the index, which determined the number of I/Os it
takes to get to the leaf blocks or the index, was sometimes minimized.
By eliminating fragments and shrinking segments in a much more automated and
online fashion, database releases since Oracle Database 10g greatly simplify solving
fragmentation problems; the result is that optimal conditions exist for performance.
Backup and Recovery
Even if you??™ve taken adequate precautions, critical database records can sometimes
be destroyed as a result of human error or hardware or software failure.
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