#no so  good
createIndex( $table, $name, $keyfield, undef, undef, 1);
createIndex( $table, $name, $keyfield, undef, 75);

#slightly better
createIndex( $table, $name, $keyfield, undef, undef, 'ignore_dup_keys' );
createIndex( $table, $name, $keyfield, undef, 'fillfactor=75' );