开启MySQL慢查询日志

1、修改my.cnf或my.ini

1)、linux-----------------------------------

/etc/my.cnf 文件

[mysqld]

long_query_time = 1
log-slow-queries XXXXXXXXX

2)、window--------------------------------

my.ini 文件

[mysqld]

long_query_time = 1
log-slow-queries=C:\mysql_slow.log;
log-queries-not-using-indexes

2、service mysql restart

3、

方法二：用 mysql 客户端命令行修改，但重启之后会失效

mysql> show variables like 'lo%';
+---------------------------------+---------------------+
| Variable_name | Value |
+---------------------------------+---------------------+
| local_infile | ON |
| lock_wait_timeout | 31536000 |
| locked_in_memory | OFF |
| log | OFF |
| log_bin | ON |
| log_bin_trust_function_creators | OFF |
| log_error | /disk/mysql/www.err |
| log_output | FILE |
| log_queries_not_using_indexes | OFF |
| log_slave_updates | OFF |
| log_slow_queries | OFF |
| log_warnings | 1 |
| long_query_time | 10.000000 |
| low_priority_updates | OFF |
| lower_case_file_system | OFF |
| lower_case_table_names | 0 |
+---------------------------------+---------------------+
16 rows in set (0.00 sec)

mysql> set global long_query_time = 1;
Query OK, 0 rows affected (0.00 sec)

mysql> set global log_slow_queries = on;
Query OK, 0 rows affected, 1 warning (0.31 sec)

mysql> set global log_queries_not_using_indexes = on;
Query OK, 0 rows affected (0.00 sec)

mysql> show variables like 'lo%';
+---------------------------------+---------------------+
| Variable_name | Value |
+---------------------------------+---------------------+
| local_infile | ON |
| lock_wait_timeout | 31536000 |
| locked_in_memory | OFF |
| log | OFF |
| log_bin | ON |
| log_bin_trust_function_creators | OFF |
| log_error | /disk/mysql/www.err |
| log_output | FILE |
| log_queries_not_using_indexes | ON |
| log_slave_updates | OFF |
| log_slow_queries | ON |
| log_warnings | 1 |
| long_query_time | 10.000000 |
| low_priority_updates | OFF |
| lower_case_file_system | OFF |
| lower_case_table_names | 0 |
+---------------------------------+---------------------+
16 rows in set (0.00 sec)

此处发现一个很奇怪的问题，long_query_time的更改似乎没有生效。

过了几分钟，再看，发现已经改过来了。

mysql> show variables like 'lo%';
+---------------------------------+---------------------+
| Variable_name | Value |
+---------------------------------+---------------------+
| local_infile | ON |
| lock_wait_timeout | 31536000 |
| locked_in_memory | OFF |
| log | OFF |
| log_bin | ON |
| log_bin_trust_function_creators | OFF |
| log_error | /disk/mysql/www.err |
| log_output | FILE |
| log_queries_not_using_indexes | ON |
| log_slave_updates | OFF |
| log_slow_queries | ON |
| log_warnings | 1 |
| long_query_time | 1.000000 |
| low_priority_updates | OFF |
| lower_case_file_system | OFF |
| lower_case_table_names | 0 |
+---------------------------------+---------------------+
16 rows in set (0.00 sec)

http://www.vktone.com/articles/usage_of_mysqldumpslow.html