如何定位并优化慢查询sql

本篇内容主要讲解“如何定位并优化慢查询sql”，感兴趣的朋友不妨来看看。本文介绍的方法操作简单快捷，实用性强。下面就让小编来带大家学习“如何定位并优化慢查询sql”吧!

• 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
  +---------------+-------+

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• 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  |
  +----+-------------+------------+------------+------+-------------------+-------------------+---------+-------+------+----------+-------+

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到此，相信大家对“如何定位并优化慢查询sql”有了更深的了解，不妨来实际操作一番吧！这里是亿速云网站，更多相关内容可以进入相关频道进行查询，关注我们，继续学习！

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