Oracle indexes do not need rebuilding on the regular basis, but only
as an exceptional event. The warning sign is when queries that utilize nested
loops slow down without any apparent reason. The only case when index needs
to be rebuilt is the case of a table with frequent delete operations. You
should consider rebuilding indexes if and only if the base table satisfies
that crieria. How to decide? There are few rules of thumb, none satisfactory
and decisive. I usually compare the number of blocks in the index with
the number of blocks in the table. If the number of blocks in the index
exceeds 50% of those in the table, the index is a candidate for rebuilding.
How did I come to 50%? I have no clue. That value popped up at one of my
previous jobs and I still use it, when I want to rebuild indexes. One of
the most frequent reasons for index rebuilding is a magazine reading boss
who has read that indexes need rebuilding. A script which rebuilds based on a
criteria like 50% of the number of blocks usually satisfies damagement,
especially if accompanied by a 3-page MS-Word document explaining this
hocus-pocus in detail. Picture of a B*-tree scanned from N. Wirth's "Data
Structures+Algorithms = Programs" is a mandatory requirement for such
documents.
On 2003.09.22 01:59, Veeraraju_Mareddi wrote:
> Dear Friends,
>
> Can somebody tell me how do we that an index needs to be rebuilt.. Different
> scenarios / any documents will be helpful.
>
> Thanks in advance.
> Rajuvera
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> Author: Veeraraju_Mareddi
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Mladen Gogala
Oracle DBA
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Received on Mon Sep 22 2003 - 01:44:48 CDT
