A FOT index is an index that is similar to a B-Tree index, but an FOT index has multiple root nodes and fewer levels. (B-Tree indexes have only one root node and more levels.)
FOT索引类似B - Tree索引，但它有多个根节点和较少的级(B - Tree索引只有一个根节点和更多的级)。
B + tree consists of a root, internal nodes and leaves. The root may be either a leaf or a node with two or more children.
树由根，内部节点和叶组成。根可以是叶或具有两个或更多个子节点的节点。
B + tree can be viewed as a B-tree in which each node contains only keys (not key-value pairs), and to which an additional level is added at the bottom with linked leaves.
树可以被视为B树，其中每个(内部)节点仅包含键(不是键值对)，并在其底部附加一层链式的叶子节点。
应用推荐