Mysql change ft_max_word_len bug

So, I have MySQL installed on my machine, and I need to change the ft_max_word_len, the maximum word length that MySQL will index. However, when I set it up via the tools provided, and query it, it still lists it as a max of 84 (I need 128+). When I try and use the command line, I get the following:

C:\>mysqld --ft_max_word_len=128
111210 23:55:46 [Warning] option 'ft_max_word_len': unsigned value 256 adjusted to 84
111210 23:55:46 [Warning] option 'ft_max_word_len': unsigned value 128 adjusted to 84

It should be noted, I tried to change it to 256 in the GUI tools, so that may be where that value is coming from. But why would I get both, and why can I not adjust this value?

Of note, I am on Windows 7, and MySQL 5.1.41 for 64bit.

Update: From @thinice's comment, this leads me to believe that this is a bug in MySQL (and from the sounds of it an mostly undocumented one, which I will need to change). So maybe my question is, would anyone have any inkling of how to change that value?

Solution 1:

The value of 84 for HA_FT_MAXCHARLEN is defined as a third of HA_FT_MAXBYTELEN (which is 254). This is defined in include/ft_global.h and changing it will mean recompiling MySQL - it is not a run-time variable. The reason it's a third is because in many character sets one character is not equal to one byte.

If you were to change HA_FT_MAXBYTELEN and recompile the tests will fail, so you're moving into unsupported-land, though your specific application may work.