How is the InnoDB index implemented?
The principle behind InnoDB index implementation is to use the B+ tree data structure to store and organize index data. B+ tree is a balanced multi-way search tree with the following characteristics:
- All leaf nodes are on the same level, connected by pointers to form an ordered doubly linked list, making it convenient for range queries.
- Non-leaf nodes do not store data, they only store index keys and references to child nodes, thus achieving hierarchical indexing.
- Each node of the B+ tree has a fixed size and can store multiple index keys, reducing the number of disk I/O operations and improving query efficiency.
- Nodes in a B+ tree are stored in order based on the size of the index key, allowing for quick location of a specified index key using binary search.
In InnoDB, each index is maintained with a B+ tree. The root node of the B+ tree is stored in memory, while non-leaf nodes and leaf nodes are stored on disk. When querying or inserting data, InnoDB quickly locates the data using the B+ tree based on the query conditions or inserted index key values.
The specific implementation process is as follows:
- Search: Starting from the root node, follow the path of the B+ tree based on the index key values. According to the size of the index key, find the appropriate child node and continue searching downwards until reaching the leaf node. The data on the leaf node is the query result.
- Insert: Starting from the root node, follow the path of the B+ tree based on the inserted index key value. Following the size of the index key, find the appropriate child node and continue to search down until reaching the suitable leaf node. Insert a new index key and corresponding data on the leaf node.
- Updating and deleting: similar to the insertion operation, once the leaf node that needs to be updated or deleted is found, the corresponding operation is performed.
By utilizing the B+ tree data structure, InnoDB can efficiently support various types of index queries and maintenance operations. In addition, InnoDB also incorporates additional technologies such as adaptive hash indexing and adaptive pre-reading to further enhance the query performance of indexes.
