将MySQL从5.5升级到5.6后查询缓慢

我们正在将mysql从5.5升级到5.6,现在某些查询的速度非常慢.

以前需要0.005秒的查询现在需要49秒.

对5.6的查询似乎跳过了索引：

+----+-------------+-------+-------+----------------------------------------------------+---------+---------+------+--------+-------------+
| id | select_type | table | type  | possible_keys                                      | key     | key_len | ref  | rows   | Extra       |
+----+-------------+-------+-------+----------------------------------------------------+---------+---------+------+--------+-------------+
|  1 | SIMPLE      | pens  | index | index_contents_on_slug,index_contents_on_slug_hash | PRIMARY | 4       | NULL | 471440 | Using where |
+----+-------------+-------+-------+----------------------------------------------------+---------+---------+------+--------+-------------+
1 row in set (0.00 sec)

但是在5.5上并没有被跳过：

+----+-------------+-------+-------------+----------------------------------------------------+----------------------------------------------------+---------+------+------+----------------------------------------------------------------------------------------------+
| id | select_type | table | type        | possible_keys                                      | key                                                | key_len | ref  | rows | Extra                                                                                        |
+----+-------------+-------+-------------+----------------------------------------------------+----------------------------------------------------+---------+------+------+----------------------------------------------------------------------------------------------+
|  1 | SIMPLE      | pens  | index_merge | index_contents_on_slug,index_contents_on_slug_hash | index_contents_on_slug_hash,index_contents_on_slug | 768,768 | NULL |    2 | Using union(index_contents_on_slug_hash,index_contents_on_slug); Using where; Using filesort |
+----+-------------+-------+-------------+----------------------------------------------------+----------------------------------------------------+---------+------+------+----------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

两个数据库都是从相同的mysql转储创建的.

在5.6上进行导入时,是否不会构建这些索引？如何强制创建索引？

查询：

SELECT  `pens`.* FROM `pens`  WHERE (slug_hash = 'style' OR slug = 'style') ORDER BY `pens`.`id` DESC LIMIT 1

编辑：删除架构

解决方法:

最终,上面接受的答案是正确的.

@RandomSeed的帮助使我朝着正确的方向思考.基本上,在5.6中创建的优化计划与在5.5中创建的优化计划大不相同,因此您可能必须像我一样对查询进行重新处理.

我没有最终使用FORCE INDEX,而是删除了查询的一部分,直到我确定是什么导致5.6丢失索引.然后,我对应用程序逻辑进行了重新设计以解决该问题.

标签：mysql-5-6,mysql,indexing,mysql-5-5
来源： https://codeday.me/bug/20191009/1880247.html