unindexed queries

Issue Summary

Hello,

I turned on log-queries-not-using-indexes on my /etc/my.cnf and i found in a day more than 65000 lines like this:

# Query_time: 0 Lock_time: 0 Rows_sent: 1 Rows_examined: 3601
SELECT hash FROM freelinking WHERE phrase = 'something';

this apparently does not cause any performance issue (but i am on a i975 quadcore so it is difficult to notice).
To reduce the indexed queries of my installation i set up an index like this:

ALTER TABLE `my_drupal`.`freelinking` ADD INDEX `phrase_key` USING HASH(`phrase`);

and afther that, no more "SELECT hash FROM..." are appended to the mysql.slow.log

This is not a bug or a performance issue, but it is a good pratice to use properly indexed queries.

The most of the times the performance issues arise as a sum of unindexed queries made to the db.

And thank you for the good module.