Is there a minimum character count on a query?

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Turns out that MySQL can be tuned to do a FULLTEXT search on smaller than 4 characters. Here are the steps:

• Edit the mysql config file (mine was /etc/my.cnf)

In the [mysqld] section, add the line:

ft_min_word_len=3

Restart mysql server and rebuild the FULLTEXT index on the answer, question and tags tables:

REPAIR TABLE answer QUICK;
REPAIR TABLE question QUICK;
REPAIR TABLE tag QUICK;

At this point, the search will return 3 letter words.

Of the tables mentioned in the solution, I can only find the tag table. The others have presumably been changed over time.

I decided to just repair all my tables -- what could it hurt? I used the myisamchk utility instead of running the REPAIR command in mysql. This seemed to work fine -- no errors when running the utility. However, afterward, there were at least two tables that were no longer correct: django_session and auth_permission.

Not until I ran the REPAIR command from a mysql prompt did these errors go away.

MySQL full text search (the only option as of Oct 2010) matches for words longer than four characters.

With PostgresQL this limitation will be removed - it's a current (as of date of this answer) development item.

There is also one quirk in the full text search right now (will probably change in the future): if you type in a query that does not have any matches, but not hit enter - nothing will change on the screen. But if you hit "enter" or press the "search" button you'll get a blank list.

That is AJAX search does not yet give any feedback when no matches are found, which can leave user with an impression that it does not work.

I've done it this way to limit screen flickering when no new useful information is found. This should be somehow fixed - with maybe a phrase "nothing found yet" and shade out search results.