Optimization of all indexes?

Question

Hello,
I know that an "alter index X coalesce" optimizes the index X. But I want to optimize all indexes of a database but I don't want to write a script with some hundred alter index statements? Is there a smart way to do this like:
for i in indexes loop
alter index i coalesce;
commit;
end loop;
(Pseudocode)
Edited by: user9206958 on 01.04.2010 01:30

Answer 1

Actually, no. If the following conditions are all true:
1.) Sequence generated key.
2.) Newest key values are inserted.
3.) Keys are updated over time.
4.) Oldest keys are deleted.
5.) Deletion doesn't skip any key values, leaving behind older key values forever.
If all the above is true, you should never need to coalesce or rebuild your indexes.
All the new key values go into the "Right hand" leaf block. On the left side, when the last key in a particular block is deleted, the empty block is left in the index structure and added back to the pool of free blocks. As a new block is needed on the right side, Oracle will grab the emptied block from the left side, unlink it from the structure, and move it to the right side.
So, in this way, blocks move from the left over to the right to be recycled. The only time this cannot happen is if some old values are left behind in the blocks on the left. (i.e. if item #5 above is not true.) If that's the case, there may be some benefit in periodic coalesces.
For more than you ever needed to know about indexes, how they work, and when index rebuilds are necessary, see Richard Foote's blog, and check out his white papers, especially "Rebuilding the Truth".
http://richardfoote.wordpress.com/
Hope that helps,
-Mark