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eyalshani

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bitmap conversion to rowid

When Oracle join a b-tree and a bitmap index
and bitmap conversion is occured.
there is from_rowid to join bitmaps,
and to_rowid to get the data from the table.
how does this from and to rowid going on?
how much does it cost? (building bitmap from rowid sounds costly)
do you have a link to a white paper on that subject?

Eyal
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renuraj

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marek_wiechula

Wow, that's an answer and half ranuraj.  I was very impressed by its completeness and the way you anticipated possible problems.  
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this is all very nice,
but you didn't answer my question.
I asked if there is a white paper which explains the alogorithm of transforming b-tree entries to bitmap entries when a bitmap from rowid occures. Please don't copy and paste the Oracle docs on bitmap indexes.

Eyal.
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There may not be a paper explaining exactly what you are asking for, but renuraj's comment clearly explains most of the advantages of bitmap indexes.  Are you just concerned about the possible performance cost of the bitmap-to-rowid conversions?  Do you have an actual situation where you have tried a bitmapped index and the performance was slower than you expected?

Stay away from bitmap indexes for most OLTP systems, but in a reporting situation, they can be very helpful.
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