Helen,
Thanks. My confusion was not about bitmap index. Anyway Kirtis explanations helped to clarify my doubts.
Shaibal
>From: "Helen J Mitchell" <[EMAIL PROTECTED]>
>Reply-To: [EMAIL PROTECTED]
>To: Multiple recipients of list ORACLE-L <[EMAIL PROTECTED]>
>Subject: Re: Bitmap Indexes
>Date: Fri, 08 Feb 2002 09:18:30 -0800
>
>Hi,
>
>Here is an article about it bitmap indexes ... I hope this gives you information.
>
>Helen
> ----- Original Message -----
> From: Shaibal Talukder
> To: Multiple recipients of list ORACLE-L
> Sent: Friday, February 08, 2002 6:58 AM
> Subject: RE: Bitmap Indexes
>
>
> Kirti,
>
> Just cureous. Normally bitmap indexes ae ae used for low cardinality columns. I am confused when you state - "Just one table uses it(bitmap index), with b-tree indexes
>
> >for PKry and one other non-unique index"
>
> If you mean - you use Bitmap index for the non unique index with b-tree index for PKey I am OK with that.
>
> Shaibal
>
> >From: "Deshpande, Kirti"
> >Reply-To: [EMAIL PROTECTED]
> >To: Multiple recipients of list ORACLE-L
> >Subject: RE: Bitmap Indexes
> >Date: Thu, 07 Feb 2002 19:58:20 -0800
> >
> >Ethan,
> > I have been using bitmap and b-tree indexes on the same table in our data
> >mart since 7.3.4. Never had a problem with query performance. Now we have
> >partitioned the tables in 8.1.7.x and most tables that were using bitmaps do
> >not need to use them anymore. Just one table uses it, with b-tree indexes
> >for PKry and one other non-unique index. No problems so far.
> > The only issue we had with bitmap indexes was the way it used up extents,
> >if those were not droppped before the dataloads. The problem still exists
> >with 8.1.7.x. Have not tried with 9i yet..
> >
> >HTH,
> >
> >- Kirti
> >
> >
> >-----Original Message-----
> >Sent: Thursday, February 07, 2002 3:07 PM
> >To: Multiple recipients of list ORACLE-L
> >
> >
> >Posted on behalf of a friend...
> >
> >
> >Fellow Oracle data warehouse DBAs (if this isn't you, you can delete this
> >note now):
> > I have a question regarding Oracle's bitmap indexes. We have been DABBLING
> >with bitmap indexes with mixed results here. In
> >many cases, they are great solutions. In some cases, where we have a mix of
> >bitmap and b-tree indexes on the same table, we occasionally get into
> >trouble --- this has to do with the Oracle optimizer deciding, on the fly,
> >to convert a regular b-tree index into a bitmap. It does this so that it
> >can AND or OR the various bitmap indexes together. Sounds great on the
> >surface but when this occurs, response time goes in the toilet.
> >
> >In one situation we have, we have a fact table with two bitmap indexes and a
> >few other b-tree indexes. A particular query we run bogs down (NEVER
> >COMPLETES) with this mix of indexes. Based on the access path that's being
> >chosen, we know which b-tree index is being converted on the fly. If we
> >convert that b-tree index into a bitmap (so we now have 3 bitmap indexes and
> >Oracle does not need to create the third one on the fly), the query really
> >runs well. If we replace the bitmap indexes with b-tree indexes (so we only
> >have b-tree indexes), we get decent response times. (This is all on Oracle
> >8.1.7.2.0, by the way.)
> >
> >I'm wondering if the rest of you data warehouse DBAs have gone "whole hog"
> >with bitmap indexes. My testing shows that when Oracle doesn't have to
> >create a bitmap index on the fly, the queries respond wonderfully. So, I'm
> >wondering if our dabbling is actually a bad validation approach and,
> >instead, we should be 'running' with LOTS bitmap indexes instead of
> >'crawling' with only a few of them. In other words, maybe we're not "taking
> >all of our medication", as someone else put it recently.
> >
> >Any insight would be most appreciated. I'm not looking for insight on the
> >query I have used as an example. I'm looking for a generalized answer that
> >says, "Yes, if you start using bitmap indexes, you should go TOTALLY to
> >bitmap indexes" or, "Hmmm, we're using some bitmap indexes and some b-tree
> >indexes and don't have the problem you have".
> >--
> >Please see the official ORACLE-L FAQ: http://www.orafaq.com
> >--
> >Author: Post, Ethan
> > INET: [EMAIL PROTECTED]
> >--
> >Please see the official ORACLE-L FAQ: http://www.orafaq.com
> >--
> >Author: Deshpande, Kirti
> > INET: [EMAIL PROTECTED]
> >
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>
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> -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: Shaibal Talukder INET: [EMAIL PROTECTED] Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051 San Diego, California -- Public Internet access / Mailing Lists -------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
><< Helenarticlerevised21_bitmap_index.doc >>
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Author: Shaibal Talukder
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