InnoDB是否有静态表？ [英] Does InnoDB have static tables?

问题描述

我正在阅读MySQL文档，并且想知道 MyISAM的静态表格格式也适用于InnoDB吗？如果我使用 CHAR 而不是 VARCHAR ，而实际长度在0到100个字符之间变化，或者是使用 VARCHAR（100）更好？

I was reading MySQL documentation and I was wondering whether MyISAM's "static" table format also applies on InnoDB or not? Do I gain performance, if I use CHAR instead of VARCHAR when the real lengths varies between 0 and 100 characters or is using VARCHAR(100) better?

推荐答案

InnoDB确实具有以下优点：宽度行，并且将表中的所有列声明为固定宽度可能会有一些好处。主要优点是页面中的所有孔都可以重复用于任何插入，因为所有行的长度均相同。这使得空间再利用效率更高。不过，我不会尝试对超过几十个字节的任何字符串强制使用固定宽度，因为每页存储额外数据的成本（因此每页较少的行数）将很快使您从更多存储中获得的节省/收益无法承受有效地重新利用空间。

InnoDB does have fixed-width rows and there can be some advantage to declaring all columns in a table as fixed-width. The main benefit is that all "holes" in a page can be reused for any insertion, since all rows are the same length. This makes space re-use somewhat more efficient. I would not try to force fixed-width for any strings over a few dozen bytes though, as the cost of storing the extra data per page (and thus fewer rows per page) would quickly overwhelm any savings/gains you'd get from more efficient space re-usage.

但是，具有固定宽度的行并不能对行扫描进行任何优化（例如， MyISAM）。 InnoDB的行存储始终基于页面，并使用具有双向链接的页面列表和页面中的单链接记录的B +树。行遍历始终使用这些结构，无法通过其他任何方式完成。

However, having fixed-width rows does not allow for any optimization of row-scanning (like it does for MyISAM) whatsoever. InnoDB's row storage is always page-based and uses a B+tree with doubly-linked lists of pages, and singly-linked records within a page. Row traversal is always using these structures and can't be done any other way.

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