Brian Hartsock's Blog

Today I ran into a very annoying MySQL issue. Basically, I can’t create a multi-part unique index for one of my tables because I get the following error.


Error executing SQL commands to update table.
MySQL Error Nr. 1071
Specified key was too long; max key length is 1024 bytes


At first, I was very confused because the multi-part index was only two VARCHAR(255) fields, which by my guess should only be 510 bytes. When googling, I found the bug report and the reason this is happening. UTF8 is reserving 3 bytes for every character, not 1 byte for every character like a typical ASCII field would.

Unfortunately, MySQL doesn’t view this as a high priority so I have to lower the length of my columns. This limitation is pretty annoying to begin with. If a user wants to hurt their performance by having very large key values, why not let them?