Foreign key values are more likely to change and other column values you have indexed may be even more volatile. Apart from that, empty space in indexes is re-used. Please read what Richard Foote has to say on the subject. Sorry to disagree, but a clean, freshly rebuild index is a happy index. Especially a bitmap index or on a volatile table. On the many databases I have managed over the past 20 years mostly data warehouse , I rebuild indexes at least monthly, unless we know the table has no dml activity.
I have seen many issues resolved by rebuilding indexes. What was common practice in older Oracle database versions is definitely NOT a good practice now!!! As another poster has underlined, except for very specific cases of mass deletions that leave many empty blocks in an index, without chance of being ever reused, it is highly NOT recommended to ever rebuild indexes.
An index with a bad structure will always revert to the same situation, and rebuilding it only causes the database to spend more time in putting things back where they were.
Thanks all for the feedback. The re-index procedure was part of the weekly procedure, to grant a better performance, logically when the tables grew and the task become of considerable time consuming, we recommend for another options such as: A if you do not need the old data just copy over another historical table.
B if you need it make partitions of your table which will improve the performance. I would employ a strategy of index rebuilds. There is very little overhead in a rebuild if you do things on indexes correctly. I know there are those that spout forth about not rebuilding but there are too many real world examples of an index rebuild solving issues for us to ignore rebuilds.
Saying that, there are some significant improvements in performance especially index scan operations and space that can be achieved on occasions.
Notably if you delete a high proportion of the data from a table, the index will not shrink unless you rebuild it, same with the underlying table. Oracle also has a tendency in some cases especially an ascending key to grow the index rather than reuse free space, which is especially annoying if you are running tight on disk space. The base table is far better at reusing space than indexes appear to be. Partitioning is really good if you have a suitable partition key.
Then you can rebuild or drop a partition rather than the entire table. For a rebuild index, it does it partition at a time rather than the entire index, so you use far less TEMP space if you have ever run out of TEMP on an index rebuild, you will know how much that hurts! With the speed that Oracle can rebuild even large and function-based indexes, its going to take a really significant index to cause a noticeable decrease in database performance.
As with hot backups, schedule them during off hours. How often you do it will be up to your needs. Every so often, we need to rebuild indexes in Oracle, because indexes become fragmented over time.
This causes their performance - and by extension - that of your database queries, to degrade. Hence, rebuilding indexes every now and again can be quite beneficial. Having said that, indexes should not be rebuilt to often, because it's a resource intensive task.
Worse, as an index is being rebuilt, locks will be placed on the index, preventing anyone from accessing it while the rebuilding occurs. Any queries trying to access this index in order to return the required results will be temporarily blocked, until the rebuild is complete.
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Oracle tuning: Blocksize and index tree structures. Determines the storage parameters used for rebuilding the spatial index data table. A spatial index data table is a regular Oracle table with a prescribed format. The following is a list of the supported subset.
Specifies the tablespace in which the index data table is created. For parallel execution you can specify an integer value of degree of parallelism. Spatial index creation involves creating and inserting index data, for each row in the underlying table column being spatially indexed, into a table with a prescribed format. All rows in the underlying table are processed before the insertion of index data is committed, and this requires adequate rollback segment space.
The ONLINE keyword rebuilds the index without blocking the index; that is, queries can use the spatial index while it is being rebuilt.
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