1. B-Trees

2. Binary Trees Binary Trees spread data all over memory
Bad for layered memory (disk/ram/cache)

3. Disk Blocks Disk data stored in blocks/sectors
Accessed in blocks of 512bytes – 4kB

4. B Trees B Tree Each node can store up to n values
Pointer between each pair of values
Max Degree = num pointers = n + 1

5. B Trees B Tree Node designed to fit block size May have degree of 100+
First level 100 keys
Second level 100,000 keys
Third level 100,000,000 keys!
Still compare against keys one at a time

6. B Tree Simulation BTree Inserts Always insert at leaves
Split at max size, median value moves to parent
Tree gets deeper when root splits

7. B Tree Simulation BTree Delete at Leaf: Remove from node Empty node
Steal from sibling via rotation if possible
Else merge with sibling & steal key from parent
Start Removed Removed 112

8. B Tree Simulation BTree Deletes At Internal Node Remove from node
Steal a replacement
Leftmost from right child or Rightmost from left child
If child underflows, merge
Start Removed Removed 119