When I look at the
EXPLAIN results, the
key len value is always calculated based on the actual column length multiplied on the maximum number of bytes for the chosen encoding. Say, for a
utf8 encoding the key len is 192.
Does this number affect performance in any way and should I reduce it when possible? I mean, does it make MySQL to reserve some space somewhere that remain unused, or it's just a maximum possible value while the used space is based on the exact data length?
So the actual question is: if I have a column that contains only Latin letters and numbers, should I change its encoding to
utf8 in regard of the space occupied by the index/overall index performance?