1. Disk access times are much slower than CPU instruction times, so minimizing disk accesses is important for performance.
2. B-trees address this issue by allowing nodes to have multiple children, reducing the height of the tree and thus the number of required disk accesses to retrieve data.
3. Keys are inserted into B-trees by adding them to leaves and splitting nodes as they become full, and deleted by removing from leaves or borrowing/promoting keys from siblings if needed to maintain minimum occupancy.
B-trees are multiway search trees used to store large datasets on disk. They reduce the height of the tree compared to binary trees, lowering the number of disk accesses needed for operations like search. A B-tree of order m has internal nodes with up to m children, keeps the leaves at the same level, and remains balanced during insertions and deletions which may involve splitting and merging nodes as well as promoting keys. B-trees are efficient for disk-based data structures due to their ability to group adjacent records into each node transfer.
B-trees are multi-way tree data structures used to store large datasets, such as an index, that are too large to fit in memory. B-trees reduce the number of disk accesses needed compared to binary trees by allowing nodes to have more than two child nodes. Keys in non-leaf nodes partition the keys in child nodes, all leaves are at the same level, and nodes are kept at least half full. Insertion and deletion may cause nodes to split or merge to maintain these properties.
The document discusses B-trees, which are tree data structures used to store large data sets that cannot fit into main memory. B-trees allow for fast retrieval of data by balancing search trees across multiple disk blocks. They work by having internal nodes with up to m children, with leaf nodes containing keys in sorted order. This balancing allows B-trees to provide fast access and search times even for very large datasets spanning multiple disk drives.
16807097.ppt b tree are a good data structureSadiaSharmin40
The document discusses B-trees, which are tree data structures used to store large datasets on disk. B-trees allow for faster retrieval of data compared to binary search trees when data exceeds main memory. B-trees differ from binary search trees in that internal nodes can have more than two child nodes and store multiple key-value pairs. The document outlines the rules for B-tree structure and provides examples of inserting and removing elements from a B-tree while maintaining its balanced structure.
The document discusses the motivation for using B-trees to store large datasets that do not fit into main memory. It notes that while binary search trees provide logarithmic-time performance, disk access times are significantly slower than memory. B-trees are designed to group related data together to minimize disk I/O and improve performance. The document defines B-trees as m-way search trees where nodes can have up to m children, leaves are on the same level, and operations like insertion and deletion involve splitting or merging nodes to balance the tree.
B-Trees are tree data structures that allow efficient retrieval of records from disk storage. They work by grouping records into pages that can be read from disk with a single access. This reduces the number of disk accesses needed compared to other tree structures when data exceeds main memory. B-Trees maintain balance by allowing nodes to have a flexible number of children within a minimum and maximum range. Keys are inserted by splitting full nodes and promoting middle keys, and deleted by borrowing from siblings or merging nodes.
This document defines and provides examples of B-trees, which are multi-way search trees used to store data in databases. B-trees allow for fast searches, insertions, and deletions. The key points are:
1. B-trees are m-way trees where each node can have up to m children. They maintain sorted keys and partition data to keep leaves at the same level.
2. An example demonstrates a 5-way B-tree containing 26 items. The process of constructing a B-tree by inserting keys one by one is also shown step-by-step.
3. Deletion from a B-tree can involve removing a key from a leaf, borrowing/prom
B-trees are multiway search trees used to store large datasets on disk. They reduce the height of the tree compared to binary trees, lowering the number of disk accesses needed for operations like search. A B-tree of order m has internal nodes with up to m children, keeps the leaves at the same level, and remains balanced during insertions and deletions which may involve splitting and merging nodes as well as promoting keys. B-trees are efficient for disk-based data structures due to their ability to group adjacent records into each node transfer.
B-trees are multi-way tree data structures used to store large datasets, such as an index, that are too large to fit in memory. B-trees reduce the number of disk accesses needed compared to binary trees by allowing nodes to have more than two child nodes. Keys in non-leaf nodes partition the keys in child nodes, all leaves are at the same level, and nodes are kept at least half full. Insertion and deletion may cause nodes to split or merge to maintain these properties.
The document discusses B-trees, which are tree data structures used to store large data sets that cannot fit into main memory. B-trees allow for fast retrieval of data by balancing search trees across multiple disk blocks. They work by having internal nodes with up to m children, with leaf nodes containing keys in sorted order. This balancing allows B-trees to provide fast access and search times even for very large datasets spanning multiple disk drives.
16807097.ppt b tree are a good data structureSadiaSharmin40
The document discusses B-trees, which are tree data structures used to store large datasets on disk. B-trees allow for faster retrieval of data compared to binary search trees when data exceeds main memory. B-trees differ from binary search trees in that internal nodes can have more than two child nodes and store multiple key-value pairs. The document outlines the rules for B-tree structure and provides examples of inserting and removing elements from a B-tree while maintaining its balanced structure.
The document discusses the motivation for using B-trees to store large datasets that do not fit into main memory. It notes that while binary search trees provide logarithmic-time performance, disk access times are significantly slower than memory. B-trees are designed to group related data together to minimize disk I/O and improve performance. The document defines B-trees as m-way search trees where nodes can have up to m children, leaves are on the same level, and operations like insertion and deletion involve splitting or merging nodes to balance the tree.
B-Trees are tree data structures that allow efficient retrieval of records from disk storage. They work by grouping records into pages that can be read from disk with a single access. This reduces the number of disk accesses needed compared to other tree structures when data exceeds main memory. B-Trees maintain balance by allowing nodes to have a flexible number of children within a minimum and maximum range. Keys are inserted by splitting full nodes and promoting middle keys, and deleted by borrowing from siblings or merging nodes.
This document defines and provides examples of B-trees, which are multi-way search trees used to store data in databases. B-trees allow for fast searches, insertions, and deletions. The key points are:
1. B-trees are m-way trees where each node can have up to m children. They maintain sorted keys and partition data to keep leaves at the same level.
2. An example demonstrates a 5-way B-tree containing 26 items. The process of constructing a B-tree by inserting keys one by one is also shown step-by-step.
3. Deletion from a B-tree can involve removing a key from a leaf, borrowing/prom
The document presents information on B-trees. It begins by defining B-trees as balanced search trees designed for storage systems that read and write large blocks of data like disks. B-trees generalize binary search trees by allowing nodes to have more than two children. They were invented to index large datasets that could not fit entirely in main memory. The document then discusses properties of B-trees like their minimum and maximum number of keys per node, search, insertion and deletion algorithms, and provides examples of constructing a B-tree.
The document discusses trees and tree data structures. It provides details on heap data structures and algorithms for inserting and deleting elements from a heap. It also covers B-trees, including their definition, properties, and algorithms for constructing, inserting, and removing elements from a B-tree. B-trees are designed to improve search efficiency for large datasets stored on disk compared to binary search trees.
B-trees are tree data structures that allow efficient retrieval of records in large datasets that exceed the capacity of main memory. B-trees allow nodes to have more than two child nodes, reducing the height of the tree and therefore the number of disk accesses needed for search, insert and delete operations compared to binary search trees. B-trees maintain the properties that all leaves are at the same depth, internal nodes have a minimum number of child nodes, and leaf nodes have a maximum number of records. This provides fast access and updates while keeping the tree balanced during operations.
B-Trees are tree data structures used to store data on disk storage. They allow for efficient retrieval of data compared to binary trees when using disk storage due to reduced height. B-Trees group data into nodes that can have multiple children, reducing the height needed compared to binary trees. Keys are inserted by adding to leaf nodes or splitting nodes and promoting middle keys. Deletion involves removing from leaf nodes, borrowing/promoting keys, or joining nodes.
The document discusses B trees and B+ trees. B trees are multi-way search trees where each node can have up to m children and keys are balanced across nodes. B+ trees are a variant where records are stored only at leaf nodes and interior nodes store keys to allow efficient data retrieval, insertion and removal. B+ trees typically store leaf nodes on disk and internal nodes in memory for large datasets.
The document defines and provides an example of a B-tree, which is a tree data structure used to store sorted data. It then walks through constructing a B-tree of order 5 by inserting keys in order. The keys are inserted into leaf nodes, and if a leaf becomes too full, it is split and the middle key is promoted. This may cause parent nodes to split as well, all the way up to the root. The root will also split if needed, increasing the height of the tree. The document concludes by listing keys to insert into an empty B-tree as an exercise.
In computer science, tree traversal (also known as tree search) is a form of graph traversal and refers to the process of visiting (checking and/or updating) each node in a tree data structure, exactly once. Such traversals are classified by the order in which the nodes are visited. The following algorithms are described for a binary tree, but they may be generalized to other trees as well.
B-Trees and B+ Trees are data structures used to store large amounts of data on disks when it cannot all fit in main memory. They allow for efficient multilevel indexing and reduce disk access times compared to other balanced trees like AVL trees by keeping the tree height low. B-Trees have multiple keys in each node and store data pointers in internal and leaf nodes, while B+ Trees only store data pointers in leaf nodes. B+ Trees provide faster searches and easier insertion/deletion compared to B-Trees. Both are commonly used in database systems and file systems to efficiently organize and retrieve large blocks of indexed data from secondary storage.
The document discusses binary trees and their traversal. It begins by defining binary trees as trees where each node has at most two children. It then discusses different binary tree terminology like left and right subtrees, root, internal and leaf nodes. Different types of binary trees are also covered like full/strict binary trees and complete binary trees. Various binary tree operations and applications are described like searching for duplicates in a list using a binary search tree. Tracing insertion of nodes in a binary search tree is also demonstrated through an example.
B+ trees are an advanced form of self-balancing trees used for indexing in databases. They improve upon B-trees by only storing data pointers in the leaf nodes, allowing for faster searches. The structure has internal nodes forming multiple levels of indexing and leaf nodes containing all key values and data pointers linked together. This allows both direct and sequential access to stored records. Operations like searching, insertion, and deletion on a B+ tree involve traversing the tree to the appropriate leaf node and rebalancing the tree if needed to maintain its properties.
This PPT is all about the Tree basic on fundamentals of B and B+ Tree with it's Various (Search,Insert and Delete) Operations performed on it and their Examples...
lecture10 date structure types of graph and terminologyKamranAli649587
The document discusses tree traversal techniques and heaps. It begins by explaining tree traversal concepts and the three common traversal techniques: preorder, inorder, and postorder. It then discusses heaps, which are almost complete binary trees where the key of each node is less than or equal to its children's keys. Heaps support efficient insertion and deletion of minimum elements in logarithmic time and are used to implement priority queues. Code implementations of binary trees, tree traversals, heaps, and their operations like insertion and deletion are also provided.
The document describes multi-way B-trees, which generalize binary search trees by allowing nodes to have multiple children. B-trees address the problem of storing large datasets that do not fit in memory by minimizing disk accesses during operations like search, insert, and delete. They achieve this through branching nodes with multiple children to reduce height, keeping leaves at the same depth, and performing splits and merges to balance the tree during modifications.
B TREE ( a to z concept ) in data structure or DBMSMathkeBhoot
B-trees are self-balancing tree data structures that keep data ordered and allow for efficient searching, insertion, and deletion operations. They improve performance for large data sets by minimizing disk accesses. Key characteristics of B-trees include being balanced, with all leaf nodes at the same level; self-balancing on insertions and deletions; and storing multiple keys per node. B-trees support efficient searching, insertion, and deletion in O(log n) time and are commonly used in databases, file systems, and other applications that require fast access to large amounts of ordered data.
The document provides information about B+ trees and height balancing trees. It begins with an introduction to B+ trees, describing their properties, representation, advantages over B-trees, and algorithms for insertion and deletion. It then covers key points about B+ trees, provides examples of height balanced trees like AVL trees and 2-3-4 trees, and gives pseudocode for operations on these trees like calculating balancing factors. The document concludes with solved problems on B+ trees.
BTrees - Great alternative to Red Black, AVL and other BSTsAmrinder Arora
BTrees - designed by Rudolf Bayer and Ed McCreight - fundamental data structure in computer science. Great alternative to BSTs. Very appropriate for disk based access.
Indexed sequential files provide both indexed and sequential access to records in a file. Records are organized into blocks, and a B+ tree index structure is used to index the blocks. This allows both efficient indexed access via the B+ tree as well as sequential access by scanning blocks. B+ trees support insertion and deletion of records through localized splitting, merging, and redistribution of blocks and index nodes to maintain balance and efficiency.
Heapsort is an O(n log n) sorting algorithm that uses a heap data structure. It works by first turning the input array into a max heap, where the largest element is stored at the root. It then repeatedly removes the root element and replaces it with the last element of the heap, and sifts it down to maintain the heap property. This produces the sorted array from largest to smallest. The heapify and reheap operations each take O(log n) time, and are performed n times, resulting in an overall time complexity of O(n log n).
Heapsort is an O(n log n) sorting algorithm that uses a heap data structure. It works by first turning the input array into a max heap, where the largest element is stored at the root. It then repeatedly removes the root element and replaces it with the last element of the heap, and sifts the new root element down to maintain the heap property. This produces a sorted array from largest to smallest in O(n log n) time.
Students can learn Trees concept in data structures. various types of data structures like binary trees, expression trees, binary search trees and AVL trees are covered in this PPT.
The document presents information on B-trees. It begins by defining B-trees as balanced search trees designed for storage systems that read and write large blocks of data like disks. B-trees generalize binary search trees by allowing nodes to have more than two children. They were invented to index large datasets that could not fit entirely in main memory. The document then discusses properties of B-trees like their minimum and maximum number of keys per node, search, insertion and deletion algorithms, and provides examples of constructing a B-tree.
The document discusses trees and tree data structures. It provides details on heap data structures and algorithms for inserting and deleting elements from a heap. It also covers B-trees, including their definition, properties, and algorithms for constructing, inserting, and removing elements from a B-tree. B-trees are designed to improve search efficiency for large datasets stored on disk compared to binary search trees.
B-trees are tree data structures that allow efficient retrieval of records in large datasets that exceed the capacity of main memory. B-trees allow nodes to have more than two child nodes, reducing the height of the tree and therefore the number of disk accesses needed for search, insert and delete operations compared to binary search trees. B-trees maintain the properties that all leaves are at the same depth, internal nodes have a minimum number of child nodes, and leaf nodes have a maximum number of records. This provides fast access and updates while keeping the tree balanced during operations.
B-Trees are tree data structures used to store data on disk storage. They allow for efficient retrieval of data compared to binary trees when using disk storage due to reduced height. B-Trees group data into nodes that can have multiple children, reducing the height needed compared to binary trees. Keys are inserted by adding to leaf nodes or splitting nodes and promoting middle keys. Deletion involves removing from leaf nodes, borrowing/promoting keys, or joining nodes.
The document discusses B trees and B+ trees. B trees are multi-way search trees where each node can have up to m children and keys are balanced across nodes. B+ trees are a variant where records are stored only at leaf nodes and interior nodes store keys to allow efficient data retrieval, insertion and removal. B+ trees typically store leaf nodes on disk and internal nodes in memory for large datasets.
The document defines and provides an example of a B-tree, which is a tree data structure used to store sorted data. It then walks through constructing a B-tree of order 5 by inserting keys in order. The keys are inserted into leaf nodes, and if a leaf becomes too full, it is split and the middle key is promoted. This may cause parent nodes to split as well, all the way up to the root. The root will also split if needed, increasing the height of the tree. The document concludes by listing keys to insert into an empty B-tree as an exercise.
In computer science, tree traversal (also known as tree search) is a form of graph traversal and refers to the process of visiting (checking and/or updating) each node in a tree data structure, exactly once. Such traversals are classified by the order in which the nodes are visited. The following algorithms are described for a binary tree, but they may be generalized to other trees as well.
B-Trees and B+ Trees are data structures used to store large amounts of data on disks when it cannot all fit in main memory. They allow for efficient multilevel indexing and reduce disk access times compared to other balanced trees like AVL trees by keeping the tree height low. B-Trees have multiple keys in each node and store data pointers in internal and leaf nodes, while B+ Trees only store data pointers in leaf nodes. B+ Trees provide faster searches and easier insertion/deletion compared to B-Trees. Both are commonly used in database systems and file systems to efficiently organize and retrieve large blocks of indexed data from secondary storage.
The document discusses binary trees and their traversal. It begins by defining binary trees as trees where each node has at most two children. It then discusses different binary tree terminology like left and right subtrees, root, internal and leaf nodes. Different types of binary trees are also covered like full/strict binary trees and complete binary trees. Various binary tree operations and applications are described like searching for duplicates in a list using a binary search tree. Tracing insertion of nodes in a binary search tree is also demonstrated through an example.
B+ trees are an advanced form of self-balancing trees used for indexing in databases. They improve upon B-trees by only storing data pointers in the leaf nodes, allowing for faster searches. The structure has internal nodes forming multiple levels of indexing and leaf nodes containing all key values and data pointers linked together. This allows both direct and sequential access to stored records. Operations like searching, insertion, and deletion on a B+ tree involve traversing the tree to the appropriate leaf node and rebalancing the tree if needed to maintain its properties.
This PPT is all about the Tree basic on fundamentals of B and B+ Tree with it's Various (Search,Insert and Delete) Operations performed on it and their Examples...
lecture10 date structure types of graph and terminologyKamranAli649587
The document discusses tree traversal techniques and heaps. It begins by explaining tree traversal concepts and the three common traversal techniques: preorder, inorder, and postorder. It then discusses heaps, which are almost complete binary trees where the key of each node is less than or equal to its children's keys. Heaps support efficient insertion and deletion of minimum elements in logarithmic time and are used to implement priority queues. Code implementations of binary trees, tree traversals, heaps, and their operations like insertion and deletion are also provided.
The document describes multi-way B-trees, which generalize binary search trees by allowing nodes to have multiple children. B-trees address the problem of storing large datasets that do not fit in memory by minimizing disk accesses during operations like search, insert, and delete. They achieve this through branching nodes with multiple children to reduce height, keeping leaves at the same depth, and performing splits and merges to balance the tree during modifications.
B TREE ( a to z concept ) in data structure or DBMSMathkeBhoot
B-trees are self-balancing tree data structures that keep data ordered and allow for efficient searching, insertion, and deletion operations. They improve performance for large data sets by minimizing disk accesses. Key characteristics of B-trees include being balanced, with all leaf nodes at the same level; self-balancing on insertions and deletions; and storing multiple keys per node. B-trees support efficient searching, insertion, and deletion in O(log n) time and are commonly used in databases, file systems, and other applications that require fast access to large amounts of ordered data.
The document provides information about B+ trees and height balancing trees. It begins with an introduction to B+ trees, describing their properties, representation, advantages over B-trees, and algorithms for insertion and deletion. It then covers key points about B+ trees, provides examples of height balanced trees like AVL trees and 2-3-4 trees, and gives pseudocode for operations on these trees like calculating balancing factors. The document concludes with solved problems on B+ trees.
BTrees - Great alternative to Red Black, AVL and other BSTsAmrinder Arora
BTrees - designed by Rudolf Bayer and Ed McCreight - fundamental data structure in computer science. Great alternative to BSTs. Very appropriate for disk based access.
Indexed sequential files provide both indexed and sequential access to records in a file. Records are organized into blocks, and a B+ tree index structure is used to index the blocks. This allows both efficient indexed access via the B+ tree as well as sequential access by scanning blocks. B+ trees support insertion and deletion of records through localized splitting, merging, and redistribution of blocks and index nodes to maintain balance and efficiency.
Heapsort is an O(n log n) sorting algorithm that uses a heap data structure. It works by first turning the input array into a max heap, where the largest element is stored at the root. It then repeatedly removes the root element and replaces it with the last element of the heap, and sifts it down to maintain the heap property. This produces the sorted array from largest to smallest. The heapify and reheap operations each take O(log n) time, and are performed n times, resulting in an overall time complexity of O(n log n).
Heapsort is an O(n log n) sorting algorithm that uses a heap data structure. It works by first turning the input array into a max heap, where the largest element is stored at the root. It then repeatedly removes the root element and replaces it with the last element of the heap, and sifts the new root element down to maintain the heap property. This produces a sorted array from largest to smallest in O(n log n) time.
Students can learn Trees concept in data structures. various types of data structures like binary trees, expression trees, binary search trees and AVL trees are covered in this PPT.
How to Setup Warehouse & Location in Odoo 17 InventoryCeline George
In this slide, we'll explore how to set up warehouses and locations in Odoo 17 Inventory. This will help us manage our stock effectively, track inventory levels, and streamline warehouse operations.
A workshop hosted by the South African Journal of Science aimed at postgraduate students and early career researchers with little or no experience in writing and publishing journal articles.
Main Java[All of the Base Concepts}.docxadhitya5119
This is part 1 of my Java Learning Journey. This Contains Custom methods, classes, constructors, packages, multithreading , try- catch block, finally block and more.
This slide is special for master students (MIBS & MIFB) in UUM. Also useful for readers who are interested in the topic of contemporary Islamic banking.
Leveraging Generative AI to Drive Nonprofit InnovationTechSoup
In this webinar, participants learned how to utilize Generative AI to streamline operations and elevate member engagement. Amazon Web Service experts provided a customer specific use cases and dived into low/no-code tools that are quick and easy to deploy through Amazon Web Service (AWS.)
2. 2
Disk access time vs CPU time
• We have assumed that all instructions are created equally in
our analysis all semester. What if this assumption is not true?
• One example:
– It could be the case that our data does not fit in memory.
– In that case we need to access the secondary storage (disk)
3. 3
A closer look at disk access
• A couple of years ago I purchased the components I need to build a home
computer. My 750g drive spins at 7200RPM and my Intel Core2 Duo runs
at 2.4 Ghz
• 7200 rpm means 7200 revolutions per minute or one revolution every
1/120 of a second (8.3ms)
• On average what we want is half way round this disk – it will take ~4ms.
– Note I am assuming the read arm is in the correct position
• This sounds good until you realize that we get 240 disk accesses a second
– the same time as 2.4 billion instructions (2.4 Ghz)
• In other words, one disk access takes about the same time as 10,000,000
instructions
• Not all instructions can be considered equal!
Note: processor speeds tend to improve at a quicker rate than
disk speeds so the cost of a disk access becomes even more
expensive as related to CPU instructions over time.
4. 4
Solution
• Assume that we use an AVL tree to store all the car driver
details in NYC (about 20 million records)
• Assume further that each node in the tree must be retrieved
from the disk.
• We still end up with a very deep tree with lots of different
disk accesses; log2 20,000,000 is about 24, so this takes about
0.1 seconds (if there is only one user of the program)
• We know we can’t improve on the log n for a binary tree
• But, the solution is to use more branches and thus less height!
• As branching increases, depth decreases
6. 6
Definition of a B-tree
• A B-tree of order m is an m-way tree (i.e., a tree where each
node may have up to m children) in which:
1. the number of keys in each non-leaf node is one less than the number
of its children and these keys partition the keys in the children in the
fashion of a search tree
2. all leaves are on the same level
3. all non-leaf nodes except the root have at least m / 2 children (int division)
4. the root is either a leaf node, or it has from two to m children
5. a leaf node contains no more than m – 1 keys
• The number m should always be odd
7. 7
An example B-Tree
51 62
42
6 12
26
55 60 70
64 90
45
1 2 4 7 8 13 15 18 25
27 29 46 48 53
A B-tree of order 5
containing 26 items
Note that all the leaves are at the same level
8. 8
Inserting into a B-Tree
• Attempt to insert the new key into a leaf
• If this would result in that leaf becoming too big, split the leaf
into two, promoting the middle key to the leaf’s parent
• If this would result in the parent becoming too big, split the
parent into two, promoting the middle key
• This strategy might have to be repeated all the way to the top
• If necessary, the root is split in two and the middle key is
promoted to a new root, making the tree one level higher
9. 9
• Suppose we start with an empty B-tree and keys arrive in the
following order:1 12 8 2 25 5 14 28 17 7 52 16 48 68
3 26 29 53 55 45
• We want to construct a B-tree of order 5
• The first four items go into the root:
• To put the fifth item in the root would violate condition 5
• Therefore, when 25 arrives, pick the middle key to make a
new root
Constructing a B-tree
1 2 8 12
10. 10
Constructing a B-tree (contd.)
1 2
8
12 25
6, 14, 28 get added to the leaf nodes:
1 2
8
12 14
6 25 28
11. 11
Constructing a B-tree (contd.)
Adding 17 to the right leaf node would over-fill it, so we take the
middle key, promote it (to the root) and split the leaf
8 17
12 14 25 28
1 2 6
7, 52, 16, 48 get added to the leaf nodes
8 17
12 14 25 28
1 2 6 16 48 52
7
12. 12
Constructing a B-tree (contd.)
Adding 68 causes us to split the right most leaf, promoting 48 to the
root, and adding 3 causes us to split the left most leaf, promoting 3
to the root; 26, 29, 53, 55 then go into the leaves
3 8 17 48
52 53 55 68
25 26 28 29
1 2 6 7 12 14 16
Adding 45 causes a split of 25 26 28 29
and promoting 28 to the root then causes the root to split
14. 14
Inserting into a B-Tree
• Attempt to insert the new key into a leaf
• If this would result in that leaf becoming too big, split the leaf
into two, promoting the middle key to the leaf’s parent
• If this would result in the parent becoming too big, split the
parent into two, promoting the middle key
• This strategy might have to be repeated all the way to the top
• If necessary, the root is split in two and the middle key is
promoted to a new root, making the tree one level higher
15. 15
Exercise in Inserting a B-Tree
• Insert the following keys to a 5-way B-tree:
• 3, 7, 9, 23, 45, 1, 5, 14, 25, 24, 13, 11, 8, 19, 4, 31, 35, 56
• Check your approach with a neighbour and discuss any
differences.
16. 16
Removal from a B-tree
• During insertion, the key always goes into a leaf. For deletion
we wish to remove from a leaf. There are three possible ways
we can do this:
• 1 - If the key is already in a leaf node, and removing it doesn’t
cause that leaf node to have too few keys, then simply remove
the key to be deleted.
• 2 - If the key is not in a leaf then it is guaranteed (by the
nature of a B-tree) that its predecessor or successor will be in
a leaf -- in this case we delete the key and promote the
predecessor or successor key to the non-leaf deleted key’s
position.
17. 17
Removal from a B-tree (2)
• If (1) or (2) lead to a leaf node containing less than the
minimum number of keys then we have to look at the siblings
immediately adjacent to the leaf in question:
– 3: if one of them has more than the min’ number of keys then we can
promote one of its keys to the parent and take the parent key into our
lacking leaf
– 4: if neither of them has more than the min’ number of keys then the
lacking leaf and one of its neighbours can be combined with their
shared parent (the opposite of promoting a key) and the new leaf will
have the correct number of keys; if this step leaves the parent with too
few keys then we repeat the process up to the root itself, if required
18. 18
Type #1: Simple leaf deletion
12 29 52
2 7 9 15 22 56 69 72
31 43
Delete 2: Since there are enough
keys in the node, just delete it
Assuming a 5-way
B-Tree, as before...
Note when printed: this slide is animated
19. 19
Type #2: Simple non-leaf deletion
12 29 52
7 9 15 22 56 69 72
31 43
Delete 52
Borrow the predecessor
or (in this case) successor
56
Note when printed: this slide is animated
20. 20
Type #4: Too few keys in node and
its siblings
12 29 56
7 9 15 22 69 72
31 43
Delete 72
Too few keys!
Join back together
Note when printed: this slide is animated
21. 21
Type #4: Too few keys in node and
its siblings
12 29
7 9 15 22 69
56
31 43
Note when printed: this slide is animated
22. 22
Type #3: Enough siblings
12 29
7 9 15 22 69
56
31 43
Delete 22
Demote root key and
promote leaf key
Note when printed: this slide is animated
23. 23
Type #3: Enough siblings
12
29
7 9 15
31
69
56
43
Note when printed: this slide is animated
24. 24
Exercise in Removal from a B-Tree
• Given 5-way B-tree created by these data (last exercise):
• 3, 7, 9, 23, 45, 1, 5, 14, 25, 24, 13, 11, 8, 19, 4, 31, 35, 56
• Add these further keys: 2, 6,12
• Delete these keys: 4, 5, 7, 3, 14
• Again, check your approach with a neighbour and discuss any
differences.
25. 25
Analysis of B-Trees
• The maximum number of items in a B-tree of order m and
height h:
root m – 1
level 1 m(m – 1)
level 2 m2(m – 1)
. . .
level h mh(m – 1)
• So, the total number of items is
(1 + m + m2 + m3 + … + mh)(m – 1) =
[(mh+1 – 1)/ (m – 1)] (m – 1) = mh+1 – 1
• When m = 5 and h = 2 this gives 53 – 1 = 124
26. 26
Reasons for using B-Trees
• When searching tables held on disc, the cost of each disc
transfer is high but doesn't depend much on the amount of
data transferred, especially if consecutive items are transferred
– If we use a B-tree of order 101, say, we can transfer each node in one
disc read operation
– A B-tree of order 101 and height 3 can hold 1014 – 1 items
(approximately 100 million) and any item can be accessed with 3 disc
reads (assuming we hold the root in memory)
• If we take m = 3, we get a 2-3 tree, in which non-leaf nodes
have two or three children (i.e., one or two keys)
– B-Trees are always balanced (since the leaves are all at the same
level), so 2-3 trees make a good type of balanced tree
27. 27
Comparing Trees
• Binary trees
– Can become unbalanced and lose their good time complexity (big O)
– AVL trees are strict binary trees that overcome the balance problem
– Heaps remain balanced but only prioritise (not order) the keys
• Multi-way trees
– B-Trees can be m-way, they can have any (odd) number of children
– One B-Tree, the 2-3 (or 3-way) B-Tree, approximates a permanently
balanced binary tree, exchanging the AVL tree’s balancing operations
for insertion and (more complex) deletion operations