> For the complete documentation index, see [llms.txt](https://docs.postgresql.tw/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.postgresql.tw/15/internals/b-tree-indexes/introduction.md).

# 67.1. Introduction

PostgreSQL 實作了標準 btree（多向平衡樹）索引資料結構。任何可以按明確定義的線性順序排序的資料型別都可以透過 btree 索引進行索引。唯一的限制是索引數目不能超過頁面的大約三分之一（如果有 TOAST 壓縮的話，指的是壓縮後的大小）。

因為每個 btree 運算子類對其資料型別強加排序順序，所以 btree 運算子類（或者，實際上，運算子家族）已經被用作 PostgreSQL 對排序的一般表示和理解。 因此，他們獲得了一些超出僅支持 btree 索引所需的功能，並且系統中與 btree AM 相距甚遠的部分使用了它們。


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