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PART 11 Multiway Search Trees

PART 11 Multiway Search Trees. B-Trees Search Insertion Deletion. AVL Trees. n = 2 30 = 10 9 (approx). 30 <= height <= 43 . When the AVL tree resides on a disk, up to 43 disk access are made for a search. This takes up to (approx) 4 seconds. Not acceptable. m-way Search Trees.

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PART 11 Multiway Search Trees

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  1. PART 11Multiway Search Trees • B-Trees • Search • Insertion • Deletion

  2. AVL Trees • n = 230 = 109(approx). • 30 <= height <= 43. • When the AVL tree resides on a disk, up to 43 disk access are made for a search. • This takes up to (approx) 4 seconds. • Not acceptable.

  3. m-way Search Trees • Each node has up to m – 1 pairs and m children. • m = 2 => binary search tree.

  4. 10 30 35 4-Way Search Tree k > 35 k < 10 10 < k < 30 30 < k < 35

  5. Maximum # Of Pairs • Happens when all internal nodes are m-nodes. • Full degree m tree. • # of nodes = 1 + m + m2 + m3 + … + mh-1 = (mh – 1)/(m – 1). • Each node has m – 1 pairs. • So, # of pairs = mh – 1.

  6. Capacity Of m-Way Search Tree

  7. Definition Of B-Tree • Definition assumes external nodes (extended m-way search tree). • B-tree of order m. • m-way search tree. • Not empty => root has at least 2 children. • Remaining internal nodes (if any) have at least ceil(m/2) children. • External (or failure) nodes on same level.

  8. B Trees • 2-3 tree is B-tree of order 3. • 2-3-4 tree is B-tree of order 4. • B-tree of order 5is3-4-5tree (root may be2-node though). • B-tree of order 2 is full binary tree.

  9. Insert 8 4 15 20 1 3 5 6 9 30 40 16 17 Insertion into a full leaf triggers bottom-up node splitting pass.

  10. Split An Overfull Node m a0 p1 a1 p2 a2 …pm am • aiis a pointer to a subtree. • piis a dictionary pair. ceil(m/2)-1 a0 p1 a1 p2 a2 …pceil(m/2)-1 aceil(m/2)-1 m-ceil(m/2) aceil(m/2) pceil(m/2)+1 aceil(m/2)+1 …pm am • pceil(m/2)plus pointer to new node is inserted in parent.

  11. Insert 8 4 15 20 1 3 5 6 9 30 40 16 17 • Insert a pair with key = 2. • New pair goes into a 3-node.

  12. 1 2 3 2 1 3 Insert Into A Leaf 3-node • Insert new pair so that the 3keys are in ascending order. • Split overflowed node around middle key. • Insert middle key and pointer to new node into parent.

  13. Insert 8 4 15 20 1 3 5 6 9 30 40 16 17 • Insert a pair with key = 2.

  14. Insert 8 4 2 15 20 3 1 5 6 9 30 40 16 17 • Insert a pair with key = 2plus a pointer into parent.

  15. 8 2 4 15 20 1 3 5 6 9 30 40 16 17 Insert • Now, insert a pair with key = 18.

  16. 16 17 18 17 16 18 Insert Into A Leaf 3-node • Insert new pair so that the 3keys are in ascending order. • Split the overflowed node. • Insert middle key and pointer to new node into parent.

  17. 8 2 4 15 20 1 3 5 6 9 30 40 16 17 Insert • Insert a pair with key = 18.

  18. Insert 8 17 2 4 15 20 18 1 3 5 6 9 16 30 40 • Insert a pair with key = 17plus a pointer into parent.

  19. Insert 17 8 2 4 15 20 1 18 3 5 6 9 16 30 40 • Insert a pair with key = 17plus a pointer into parent.

  20. 8 17 2 4 15 20 1 18 3 5 6 9 16 30 40 Insert • Now, insert a pair with key = 7.

  21. Insert 8 17 6 2 4 15 20 7 1 18 3 5 9 16 30 40 • Insert a pair with key = 6plus a pointer into parent.

  22. Insert 8 17 4 6 2 15 20 5 7 18 9 16 30 40 1 3 • Insert a pair with key = 4plus a pointer into parent.

  23. Insert 8 4 17 6 2 15 20 1 3 5 7 18 9 16 30 40 • Insert a pair with key = 8plus a pointer into parent. • There is no parent. So, create a new root.

  24. Insert 8 4 17 6 2 15 20 18 9 16 30 40 1 3 5 7 • Height increases by 1.

  25. Delete A Pair • Deletion from interior node is transformed into a deletion from a leaf node. • Deficient leaf triggers bottom-up borrowing and node combining pass. • Deficient node is combined with an adjacent sibling who has exactly ceil(m/2) – 1 pairs. • After combining, the node has [ceil(m/2) – 2] (original pairs) + [ceil(m/2) – 1] (sibling pairs) + 1 (from parent) <= m –1 pairs.

  26. Exercises • Page 623, Problem 2 • Page 623, Problem 3 • Page 623, Problem 4 • Page 623, Problem 5

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