问题
I know that limiting the row size will keep the size at a set maximum, however, if i limit all my rows to the maximum that they will ever need, does that increase performance on the rows (i.e. take up less space)
Or does mysql dynamically allocate the size necessary for rows and maximum row length has no affect on it?
回答1:
MySQL will not dynamically size fields; the potential required size is determined by the data type you choose. However, you can choose appropriate data types to help optimize the database.
For example, the TINYINT, SMALLINT, MEDIUMINT, INT, and BIGINT data types require 1 byte, 2 bytes, 3 bytes, 4 bytes, and 8 bytes respectively. If you are only ever going to store integers up to 10,000, SMALLINT would be the best choice since it can store values up to 65,535 (unsigned) wioth plenty of extra room and requires half of the size of an INT.
With variable length types like VARCHAR any length up to and including 255 uses a one byte prefix to store the length. Anything more uses a 2 byte prefix. Limiting VARCHARs to at most 255 if possible is best. As an example, the string foo will require 4 bytes in both a VARCHAR(3) field and a VARCHAR(255) field. If the max length of the field was 500, for example, foo would require 5 bytes.
When possible with short (or sometimes even long) text xolumns, the CHAR type can be beneficial if the strings always have the same length or a very close length. Also, if you're using the MyISAM storage engine and all of your columns are fixed length, you can use the FIXED row format, which is beneficial.
More information about the MySQL data types is available in the manual.
回答2:
I don't know what is purpose of your question, but if you want to minimize storage space used by database you may use built-in compression, which is avaliable when you are using InnoDB storage engine.
More information: Enabling Compression for a Table (dev.mysql.com)
I don't know how it affects performance (speed), I never used that feature, but I think compression may slow your database significantly. However if you have limited disk space on some hosting server - it may be useful for applictions without heavy load.
回答3:
MySql does not automatically allocate the necessary size, so you wan't to define it yourself to make the database's performance better and keeping it at a minimum size.
One nice approach that I walked into the other way though was to use NVARCHAR instead of VARCHAR if the VARCHAR was to be used for long strings, but yet not long enough to fit for TEXT, which requires a lot of space.
来源：https://stackoverflow.com/questions/15104093/does-limiting-the-size-of-rows-benefit-mysql-table-size