数据库系统概念示例

B+树

相应的b -树

In a B tree search keys and data are stored in internal or leaf nodes. But in a B+-tree data is stored only in leaf nodes. Full scan of a B+ tree is very easy because all data are found in leaf nodes. Full scan of a B tree requires a full traversal. In a B tree, data may be found in leaf nodes or internal nodes. Deletion of internal nodes is very complicated. In a B+ tree, data is only found in leaf nodes. Deletion of leaf nodes is easy. Insertion in B tree is more complicated than B+ tree. B+ trees store redundant search keys but B tree has no redundant value. In a B+ tree, leaf node data is ordered as a sequential linked list but in a B tree the leaf node cannot be stored using a linked list. Many database systems' implementations prefer the structural simplicity of a B+ tree.

The primary distinction between B-tree and B+tree is that B-tree eliminates the redundant storage of search key values.Since search keys are not repeated in the B-tree,we may not be able to store the index using fewer tree nodes than in corresponding B+tree index.However,since search key that appear in non-leaf nodes appear nowhere else in B-tree,we are forced to include an additional pointer field for each search key in a non-leaf node. Their are space advantages for B-tree, as repetition does not occur and can be used for large indices.

定义“快得多”。渐近地它们是相同的。不同之处在于它们如何使用二级存储。维基百科上关于B-树和B+树的文章看起来相当可信。

数据库系统概念示例

B+树

相应的b -树

B+树的一个可能的用途是它适用于各种情况 哪里的树长得太大，以至于它不适合可用 内存。因此，您通常期望执行多个I/O。 B+树确实经常被使用，即使它实际上适合 内存，然后你的缓存管理器可能会永久保存它。但 这是一个特殊的情况，而不是一般的情况，缓存策略是 与B+树的维护分开。

另外，在B+树中，叶子页以 一个链表(或双链表)，用于优化遍历 (用于范围搜索、排序等)。所以指针的数量是 所使用的特定算法的函数。