理解 MySQL MyISAM ROW_FORMAT=DYNAMIC
Understanding MySQL MyISAM ROW_FORMAT=DYNAMIC
我有一个 MyISAM table，只有 1600 列整数类型（tinyint、smallint、mediumint、int）。 table 有 80 万行。
ROW_FORMAT=FIXED => 二进制文件大小 = 3GB（= 预期值）
ROW_FORMAT=DYNAMIC => 二进制文件大小 = 200MB
为什么文件大小会改变，因为所有列 （请不要问我列数） 的长度是固定的？
零值以动态格式优化。来自 documentation:
Each row is preceded by a bitmap that indicates which columns contain the empty string (for string columns) or zero (for numeric columns). This does not include columns that contain NULL values. If a string column has a length of zero after trailing space removal, or a numeric column has a value of zero, it is marked in the bitmap and not saved to disk. Nonempty strings are saved as a length byte plus the string contents.
所以大小差异表明您 table 中的大部分值都是零。
我有一个 MyISAM table，只有 1600 列整数类型（tinyint、smallint、mediumint、int）。 table 有 80 万行。
ROW_FORMAT=FIXED => 二进制文件大小 = 3GB（= 预期值）
ROW_FORMAT=DYNAMIC => 二进制文件大小 = 200MB
为什么文件大小会改变，因为所有列 （请不要问我列数） 的长度是固定的？
零值以动态格式优化。来自 documentation:
Each row is preceded by a bitmap that indicates which columns contain the empty string (for string columns) or zero (for numeric columns). This does not include columns that contain NULL values. If a string column has a length of zero after trailing space removal, or a numeric column has a value of zero, it is marked in the bitmap and not saved to disk. Nonempty strings are saved as a length byte plus the string contents.
所以大小差异表明您 table 中的大部分值都是零。