on 04-14-2012 1:26 PM
hi,
can any one plz explain me in detail about bit map and b tree index ??? where we use this???
difference between both???
Hi Venkat,
Bit map and B tree indexes are related to cardinality.
Cardinality means no. of pre defined objetcs for a specific infoobject.
Bit map is used when low cardinality exist. Takes fraction of space compered to B tree indexing
Very less index creation time
B tree is used for high cardinality.
Regards,
Shilpa
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Hi,
Bit map and B-tree index - It is related to Cardinality. Cardinality means no. of predefined options for perticular Info Object.
Ex: Sex of person - Male or Female - we have only two options - so it will be considered as Low Cardinality.
Document Number : their can be many document numbers depends on the no. of users. so it is considered as high cardinaltiy.
If low cardinality is their, Bit map index is used.
If high cardinalty is their, B tree index is used.
Line Item & High Cardinality :
If the size of dimension is 30% of the Size of Fact table, we should consider this dimension as Line Item dimention.
We can check the same in RSRT.
High Cardinalty - I have already explained above.
If high cardinality dimension crosses size of 30% size of fact table, convert that dimension to Line item dimension.
Check this links...
http://www.citagus.com/citagus/blog/bitmap-vs-b-tree-index-performance-comparison/
Regards,
Aravind.
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thanks shilpa gudumasu, Aravind Nag M
u guys said about both but wats the definitions for them????
Hi,
Bitmap index
A bitmap index uses maps of bits to locate records in a table. Bitmap indices are very effective for Boolean operations of the WHERE clause of a SELECT statement. When the cardinality of a column is low, a bitmap index size will be small, thereby reducing I/O volume.
Check this links you will have better understanding...
http://scn.sap.com/thread/1523790
Regards,
Aravind.
Hi
With the help of below links and images you will get clear idea
http://en.wikipedia.org/wiki/Bitmap_index
http://stackoverflow.com/questions/3607471/how-does-a-bitmap-index-work
Regards,
Venkatesh
Hi Venkatesh
As Aravind said, bitmap index uses maps of bits to locate records in a table.
A B-tree is a method of placing and locating files in the form of a tree (root and leaf nodes) where data has been sorted and allows searches, sequential access, insertions, and deletions in logarithmic time
This is how a Bitmap indices and Btree works on a string.
Bitmap
BTree
Check the details of B-tree
http://lcm.csa.iisc.ernet.in/dsa/node122.html
http://www.virtualmachinery.com/btreeguide.htm
Regards
Chandu
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