RE: Histogram VS bitmap index

Wait...Wait.... Wait....

Do I get it correct? To my understanding BITMAP and BTREE are entirely = the
different types of indexes. BTREE being the default of Oracle unless = you
specify BITMAP keyword. For a gender column, I think Bitmap is the most suitable type of index. I am sorry that Histogram are new to me, if you could possibly shed some light on it.

Refer to the following extract form Oracle Commands Manual

Creating Bitmap Indexes

Bitmap indexes store the ROWIDs associated with a key value as a = bitmap.
Each bit in the bitmap corresponds to a possible ROWID, and if the bit = is
set, it means that the row with the corresponding ROWID contains the = key
value. The internal representation of bitmaps is best suited for applications with low levels of concurrent transactions, such as data warehousing.
See Oracle8 Concepts and Oracle8 Tuning for more information about = using
bitmap indexes.

Regards,

Aleem

		-----Original Message-----
		From:	paquette stephane
[mailto:stephane_paquette_at_yahoo.com]
		Sent:	30 May, 2000 3:52 PM
		To:	Multiple recipients of list ORACLE-L
		Subject:	Re: Histogram VS bitmap index

		Hi Luc,

		In applications I've worked on, gender was always near
		a 50/50 distribution, in that case an index (btree or
		bitmap) or an histogram are not useful.

		The case where an index can help on this kind of data
		is when you have a value with very few occurences and
		your queries are looking for that value most of the
		time.

		For example if the data has the following distribution
		A 35%
		B 1%
		C 30%
		D 34%

		If your queries are looking for value B then an index
		on the column can help.




		--- Luc Demanche <ldemanch_at_cetelem.fr> a =E9crit : >
		Hello,
		>=20


		> I have an EMP table with a field named GENDER.  The

		> only two

		> possibilities

		> for this field is M or F.

		>=20


		> What is the best strategy for the cost optimizer

		> between:

		>=20


		> 1- Create a column histogram on GENDER

		> 2- Create a bitmap index on GENDER

		>=20


		> We don't use bind variables for GENDER (important