Question

I am just starting to investigate optimization for my MySQL database. From what I’m reading, indexing seems like a good idea – so I am wanting to create an index on one of my VARCHAR columns, on a table using the MyISAM engine.

From what I’m reading, I understand that an index is limited to a size of 1,000 bytes. A VARCHAR character is 3 bytes in size, though. Does that mean that if I want to index a VARCHAR column with 50 rows, I need an index prefix of 6 characters? (1,000 bytes / 50 rows / 3 bytes per character = 6.66)

If so, that seems a little comiplicated – which is why I’m questioning my understanding. It seems pretty odd that you would only be able to index 333 rows in a VARCHAR column, using a prefix of 1 character.

Am I missing something?

Answer 1

From what I’ve read, I understand that an index is limited to a size of 1000 bytes.

Index key length is limited to 1000 bytes in MyISAM, 767 bytes in InnoDB (per column).

This means that you cannot index a single UTF8 column more than 333 characters long in a MyISAM table (when calculating the max index size, MySQL assumes 3 bytes per character, though actual length may be much smaller)

You can create as many indexed records as you need.