定位并优化慢查询sql

根据慢日志定位慢查询sql

mysql> show variables like "%query%";
+------------------------------+-------------------------------------------------+
| Variable_name                | Value                                           |
+------------------------------+-------------------------------------------------+
| binlog_rows_query_log_events | OFF                                             |
| ft_query_expansion_limit     | 20                                              |
| have_query_cache             | YES                                             |
| long_query_time              | 10.000000                                       |    查询时间
| query_alloc_block_size       | 8192                                            |
| query_cache_limit            | 1048576                                         |
| query_cache_min_res_unit     | 4096                                            |
| query_cache_size             | 1048576                                         |
| query_cache_type             | OFF                                             |
| query_cache_wlock_invalidate | OFF                                             |
| query_prealloc_size          | 8192                                            |
| slow_query_log               | OFF                                             | .  慢日志是否打开
| slow_query_log_file          | /usr/local/mysql/data/tandeMacBook-Pro-slow.log |    慢日志log位置
+------------------------------+-------------------------------------------------+


mysql> set global show_query_log = on;   开启慢查询日志（最好写在配置文件）
mysql> set global long_query_time = 1;   设置慢日志查询时间


mysql> show status like "%slow_queries%";
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| Slow_queries  | 0     |    慢查询出现的次数
+---------------+-------+

使用explain等工具分析sql

mysql> explain select * from t_employee where name = "汪燕";
+----+-------------+------------+------------+------+-------------------+-------------------+---------+-------+------+----------+-------+
| id | select_type | table      | partitions | type | possible_keys     | key               | key_len | ref   | rows | filtered | Extra |
+----+-------------+------------+------------+------+-------------------+-------------------+---------+-------+------+----------+-------+
|  1 | SIMPLE      | t_employee | NULL       | ref  | idx_employee_name | idx_employee_name | 50      | const |    1 |   100.00 | NULL  |
+----+-------------+------------+------------+------+-------------------+-------------------+---------+-------+------+----------+-------+

修改sql或者尽量让sql走索引