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Searching in a B-tree

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Slideshow:

Lookup in a B⁺-tree: internal nodes

Lookup in a B⁺-tree: internal nodes

Lookup in a B⁺-tree: leaf node

The index file is stored in the leaf nodes
If search key is not found in the leaf node, the data does not contain the search key !!
Example of lookup in a B⁺-tree
         
Find the record containing the search key 40
Example of lookup in a B⁺-tree

Find the record containing the search key 40: 40 not found - data is not in file !
Example of lookup in a B⁺-tree
         
Find the record containing the search key 41
Example of lookup in a B⁺-tree

Find the record containing the search key 41: 41 found - follow DB address in index to record
Next: maintaining a B⁺-tree
How to insert a new search key in a B+-tree      How to delete a search key in a B+-tree
 
We must maintain the structural requirements and occupancy constraints of the B⁺-tree !!!
The B⁺-tree must remain balanced !!!
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• Lookup in a B-tree
  • Search for a record with search key = x:

    Start at the root node use a linear search to find the next node as follows: Follow one of the pointers to the next node Repeat this step as long as the next node is an internal node When you reached a leaf node: Search for the key = x: If x is found: Use the block/record pointer to fetch x If x is not found: Report a x not found error

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  • Example: search for search key = 40

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  • Example: search for search key = 41