求助, mysql所有查询都变成了慢查询, 但是在mysql client里面又很快

# User@Host: lengxiaohua[lengxiaohua] @ localhost []
# Query_time: 43.612502 Lock_time: 0.000000 Rows_sent: 0 Rows_examined: 0
SET timestamp=1372129298;
commit;


# Time: 130625 11:01:39
# User@Host: lengxiaohua[lengxiaohua] @ localhost [127.0.0.1]
# Query_time: 0.242507 Lock_time: 0.000045 Rows_sent: 1 Rows_examined: 113883
SET timestamp=1372129299;
select * from User where LOWER(email)='[email protected]' limit 1;


# User@Host: lengxiaohua[lengxiaohua] @ localhost [127.0.0.1]
# Query_time: 42.509005 Lock_time: 0.000036 Rows_sent: 0 Rows_examined: 1
SET timestamp=1372129298;
update User set login_count = login_count +1 where Userid=116881;

上面是慢查询日志, 同样的sql语句复制到终端里面运行是0.00秒, 但是mysql的io负载很高, 不知道如何分析优化mysql, 求助