1.先查看目前日志输出方式
show variables like '%log_output%';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| log_output | FILE |
+---------------+-------+
log_output 参数设定日志文件的输出，可选值为 TABLE, FILE ,NONE; "TABLE" 意思为设定日志分别记录到 mysql 库的 general_log 和 slow_log 表中; "FILE" 意思为记录日志到操作系统的文件中， "NONE" 意思为取消日志记录。
set global log_output='FILE,TABLE';
2.查看慢日志是否开启
show variables like '%slow%';
+---------------------+------------------------------------+
| Variable_name | Value |
+---------------------+------------------------------------+
| log_slow_queries | ON |
| slow_launch_time | 2 |
| slow_query_log | ON |
| slow_query_log_file | /ssddata2/mysql/3306/logs/slow.log |
+---------------------+------------------------------------+
3.设置开启慢日志
set global log_slow_queries = on;
4.查询没有index的查询记录开关
show global variables like '%indexes%';
+----------------------------------------+-------+
| Variable_name | Value |
+----------------------------------------+-------+
| log_queries_not_using_indexes | OFF |
| log_throttle_queries_not_using_indexes | 0 |
+----------------------------------------+-------+
第一个参数 表示是否开启记录没有index的查询，第二个
参数用来做日志记录的流量控制，一分钟可以记录多少条，默认0是表示不限制。
5.修改慢日志存储路径
set global slow_query_log_file = '/ssddata2/mysql/3306/logs/slow.log'；
6.设置慢日志记录时间
show variables like "%long%"
+-----------------+----------+
| Variable_name | Value |
+-----------------+----------+
| long_query_time | 5.000000 |
+-----------------+----------+
set global long_query_time = 5;
slow_launch_time的设定跟慢查询日志的查询阀值设定不同，表示了thread create的一个阀值，如果thread create的时间超过了这个值，这变量slow_launch_time的值加1.
而设置Long_query_time表示超过多少秒的查询就写入日志，默认的是10s,设置为0的话表示记录所有的查询。
7.管理型SQL可以通过--log-slow-admin-statements开启记录管理型慢SQL
a. The query must either not be an administrative statement, or --log-slow-adminstatements must have been specified.
b. The query must have taken at least long_query_time seconds, or log_queries_not_using_indexes must be enabled and the query used no indexes for row lookups.
c. The query must have examined at least min_examined_row_limit rows.
d. The query must not be suppressed according to the log_throttle_queries_not_using_indexes setting.