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To Bitmap or not to Bitmap - that is the question

From: Dipen Kotecha <dkotecha_at_ford.invalid>
Date: Tue, 12 Oct 1999 13:55:28 +0200
Message-ID: <380321B0.A74814DF@ford.invalid>


Hi,

I am looking for some advice on bitmap indexes. I currently have a query that is using a bitmap index and a non-bitmap index. It is doing a 'bitmap conversion' before doing the 'bitmap AND' and then a 'bitmap conversion' again (see explain plan below).

OPERATION                      OPTIONS        OBJECT NAME         
ORDER     

------------------------------ -------------- --------------------
----------
INSERT STATEMENT COST = 18294 0-0-18294 SORT GROUP BY 1-0-1 NESTED LOOPS 2-1-1 TABLE ACCESS FULL T_DID_LOAD 3-2-1 TABLE ACCESS BY ROWID T_ENTITY 4-2-2 BITMAP CONVERSION TO ROWIDS 5-4-1 BITMAP AND 6-5-1 BITMAP CONVERSION FROM ROWIDS 7-6-1 INDEX RANGE SCAN T_DEALERCODE_IDX 8-7-1 BITMAP INDEX SINGLE VALUE T_COUNTRY_ID_BIT_IDX 9-6-2

Now my question is :

What is the performance degradation in converting a non bitmap index to bitmap and back again? Would it be better for me to rebuild the dealercode index to bitmap, or the country_id index to non bitmap?

I am using Oracle 7.3.4. The T_ENTITY table has 1.5 million rows. There are 50 distinct dealercodes and 20 distinct country_id's. Neither are uniformly distributed.

Thanks in advance,

Dipen Received on Tue Oct 12 1999 - 06:55:28 CDT

Original text of this message

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