Re: B-Tree Index Vs Bitmap Index Question

From: <rtgraf_at_my-dejanews.com>
Date: Tue, 28 Jul 1998 06:19:58 GMT
Message-ID: <6pjqie$rgm$1@nnrp1.dejanews.com>

In article <6peem7$s58$1_at_news.nuri.net>,   "Bong Hyun Kim" <haunter_at_nuri.net> wrote:
> Hi there,
>
> Does any one know what is difference between B-Tree Index and
> Bitmap Index on Oracle 8 Server ?
> Thanks.
>
> B.H.Kim
>
>

(Leaving out technical details and CREATE INDEX stmts.) B-Tree Indexes are structured as trees: The indexed columns are arranged in a tree-like fashion using the key values as interval markers. The leaves of these trees contain the ROWIDs of the rows in the indexed table.
Bitmap Indexes are substantially different: They can be imagined as tables of 1s and 0s.
If the bitmapped column in a table of 1000000 rows contains just a few different values, bitmapped indexes can speed up retrieval a lot. (In this scenario, btree indexes won't help) For each value, you have a (compressed) sequence of 1s and 0s that indicate the ROWIDs that contain the resp. values.

Hope this helps.
--
Robert Graf-Waczenski

---

e-mail: rtgraf_at_sintec.de
Visit our web site: http://www.sintec.de

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