MySQL Type Performance (varchar vs text)

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Great article about the difference between the varchar type and the text type in MySQL.

To quote (emphasis added):

[L]et’s start out with the two new VARCHAR(30000) columns.  In a normal MyISAM table, with a dynamically sized row, these two columns only take as much space as the data they contain (plus 1 byte).  That is, if I had a row and these two columns only had 10 bytes of data in them, the row size would be (10+1)*2+[other columns].  However, if I happened to convert this MyISAM table to use fixed-length rows, or I was using the MEMORY storage engine, the row size would be 30000*2+[other columns].  Currently, according to my dataset, these dynamically sized rows only required an average of 1,648 bytes per row.

The full article can be viewed here.


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