MySQL语句执行需要超过一分钟 [英] MySQL statement takes more than minute to execute

问题描述

我正在一个数据库很大的网站上工作.当时表中有1百万条记录.当我执行查询时，这将花费太多时间来执行.下面是一个示例查询:

I am working on a website in which the database is huge. 1 million records are in the table at the time. When I perform a query then it takes too much time to execute. One sample query is given below:

select * from `ratings` order by id limit 499500, 500

每个查询都需要一分钟以上的时间，但是当我将表放到1万条记录中时，该查询就会快速执行.

Every query takes more than one minute, but when I drop the table to 10 thousand records then this query executes fastly.

正如我所读过的那样，表中的一百万条记录没有问题，因为在数据库表中没有大记录的问题.

As I have read that there is not problem for 1 million records in a table because in database tables, there is not problem of big records.

我已经通过堆栈溢出问题

I have used indexing of id in the table by the help of Stack Overflow question How do I add indices to MySQL tables?, but still I got the same problem.

***我在项目中使用 CodeIgniter .

*** I am using CodeIgniter for the project.

推荐答案

注意，这并不是建议您过一会儿再使用MyISAM.我只使用它来获取我的ID，最小值，最大值和计数以排队.所以请忽略引擎.

Note, this is not suggesting for a minute to use MyISAM. I use that only to get my ids, min,max, and count to line up. So ignore the engine, please.

create table ratings
(   id int auto_increment primary key,
    thing int null
)engine=MyISAM;
insert ratings (thing) values (null),(null),(null),(null),(null),(null),(null),(null),(null);
insert ratings (thing) select thing from ratings;
insert ratings (thing) select thing from ratings;
insert ratings (thing) select thing from ratings;
insert ratings (thing) select thing from ratings;
insert ratings (thing) select thing from ratings;
insert ratings (thing) select thing from ratings;
insert ratings (thing) select thing from ratings;
insert ratings (thing) select thing from ratings;
insert ratings (thing) select thing from ratings;
insert ratings (thing) select thing from ratings;

insert ratings (thing) select thing from ratings;
insert ratings (thing) select thing from ratings;
insert ratings (thing) select thing from ratings;
insert ratings (thing) select thing from ratings;
insert ratings (thing) select thing from ratings;
insert ratings (thing) select thing from ratings;
insert ratings (thing) select thing from ratings;

insert ratings (thing) select thing from ratings;
insert ratings (thing) select thing from ratings;

我现在有470万行

select count(*),min(id),max(id) from ratings;
+----------+---------+---------+
| count(*) | min(id) | max(id) |
+----------+---------+---------+
|  4718592 |       1 | 4718592 |
+----------+---------+---------+
select * from `ratings` order by id limit 499500, 500;
-- 1 second on a dumpy laptop

.

explain select * from `ratings` order by id limit 499500, 500;
+----+-------------+---------+------+---------------+------+---------+------+---------+----------------+
| id | select_type | table   | type | possible_keys | key  | key_len | ref  | rows    | Extra          |
+----+-------------+---------+------+---------------+------+---------+------+---------+----------------+
|  1 | SIMPLE      | ratings | ALL  | NULL          | NULL | NULL    | NULL | 4718592 | Using filesort |
+----+-------------+---------+------+---------------+------+---------+------+---------+----------------+

.

explain select * from `ratings` where id>=499501 limit 500;
+----+-------------+---------+-------+---------------+---------+---------+------+---------+-----------------------+
| id | select_type | table   | type  | possible_keys | key     | key_len | ref  | rows    | Extra                 |
+----+-------------+---------+-------+---------------+---------+---------+------+---------+-----------------------+
|  1 | SIMPLE      | ratings | range | PRIMARY       | PRIMARY | 4       | NULL | 4198581 | Using index condition |
+----+-------------+---------+-------+---------------+---------+---------+------+---------+-----------------------+

故事的寓意可能是使用where子句.

Moral of the story may be to use a where clause.

不能排除出现僵局的可能性.

One cannot rule out the possibility of a deadlock.

这篇关于MySQL语句执行需要超过一分钟的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！