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MySQL ERROR 1040: Too many connections

来源：SegmentFault 2023-02-16 15:21:48 0浏览收藏

本篇文章向大家介绍《MySQL ERROR 1040: Too many connections》，主要包括MySQL、MySQL优化，具有一定的参考价值，需要的朋友可以参考一下。

如题，本章主要讲下当服务器出现

## 查看最大连接数
SHOW VARIABLES LIKE "max_connections";
+-----------------+-------+
| Variable_name   | Value |
+-----------------+-------+
| max_connections | 512   |
+-----------------+-------+

## 查看已使用最大连接数
SHOW VARIABLES LIKE 'Max_used_connections';
+----------------------+-------+
| Variable_name        | Value |
+----------------------+-------+
| Max_used_connections | 499   |
+----------------------+-------+

处理方案

这个问题一般有两种处理方案，解决方案非常容易，我们只需要增加

SET GLOBAL max_connections = 1000;

上面mysql连接值临时增加到1000，但仅适用于当前会话。一旦我们重新启动mysql服务或重新启动系统，该值将重置为默认值。

永久增加mysql最大连接数

为了永久增加mysql连接数，我们需要编辑mysql配置文件，即

## 修改
max_connections = 1000

保存文件重启MySQL即可生效。

扩多少合适？

innodb_buffer_pool_size
+ key_buffer_size
+ max_connections * (sort_buffer_size + read_buffer_size + binlog_cache_size)
+ max_connections * 2MB

方式二

安装比例扩容：

max_used_connections / max_connections * 100% = [85, 90]%

SHOW STATUS LIKE  'Threads%';
+-------------------+--------+
| Variable_name     | Value  |
+-------------------+--------+
| Threads_cached    | 1      | 
| Threads_connected | 217    |
| Threads_created   | 29     |
| Threads_running   | 88     |
+-------------------+--------+

SHOW VARIABLES LIKE 'thread_cache_size';
+-------------------+-------+
| Variable_name     | Value |
+-------------------+-------+
| thread_cache_size | 10     |
+-------------------+-------+

Threads_cached 线程在缓存中的数量
Threads_connected 当前打开的连接数
Threads_created 创建用于处理连接的线程数。
Threads_running 未休眠的线程数

如果Threads_created大，则可能要增加thread_cache_size值。缓存未命中率可以计算为Threads_created / Connections

查看表锁情况

SHOW GLOBAL STATUS LIKE 'table_locks%';
+-----------------------+-------+
| Variable_name         | Value |
+-----------------------+-------+
| Table_locks_immediate | 90    |
| Table_locks_waited    | 0     |
+-----------------------+-------+

Table_locks_immediate 立即获得表锁请求的次数
Table_locks_waited 无法立即获得对表锁的请求的次数，需要等待。这个值过高说明性能可能出现了问题，并影响连接的释放

慢查询

show variables like '%slow%';

+---------------------------+----------------------------------------------+
| Variable_name             | Value                                        |
+---------------------------+----------------------------------------------+
| slow_launch_time          | 2                                            |
| slow_query_log            | On                                           |
+---------------------------+----------------------------------------------+

线程详情

## 查看每个线程的详细信息
SHOW PROCESSLIST;
+--------+----------+------------------+--------------+---------+-------+-------------+------------------+
| Id     | User     | Host             | db           | Command | Time  | State       | Info             |
+--------+----------+------------------+--------------+---------+-------+-------------+------------------+
|      3 | xxxadmin | localhost        | NULL         | Sleep   |     1 | cleaning up | NULL             |
|      4 | xxxadmin | localhost        | NULL         | Sleep   |     0 | cleaning up | NULL             |
|      5 | xxxadmin | localhost        | NULL         | Sleep   |     6 | cleaning up | NULL             |
+--------+----------+------------------+--------------+---------+-------+-------------+------------------+