May 2020
Beginner to intermediate
319 pages
7h 3m
Chinese
Content preview from 数据库系统内幕
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54
｜
第
3
章
•
数据记录的数据（以字节表示）
0 1 5 ...
+--------------+----------------+
| [byte] flags | [int] key_size |
+--------------+----------------+
5 9 .. + key_size
+------------------+--------------------+----------------------+
| [int] value_size | [bytes] key | [bytes] data_record |
+------------------+--------------------+----------------------+
你可能已经注意到了
偏移量
和
页
ID 之间的区别。由于页大小是固定的，并且页由页缓
存来管理（参见 5.1 节），我们只需要存储页 ID 即可，使用时再通过查找表将其转换成
真正的文件偏移量。
单元格偏移量
是页局部的概念，它是相对于页起始位置的偏移量：
因此，我们可以使用比较小的整数基数，从而使格式更紧凑。
变长数据
单元格中的键和值不一定是定长的，它们都可以是变长的，其位置可以通过偏移量
从定长的单元格头部计算得到。
要找到一个键，我们需要跳过单元格的头部，读取 key_size 个字节。类似地，
要找到一个值，我们可以跳过单元格的头部再加上 key_size 个字节，然后读取
value_size 个字节。
有多种方法可以做到这一点，例如：先保存总长度，再用减法算出值的长度。这些 ...
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I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.