MySQL 8.0新特性 — 管理端口的使用简介

下面这个报错，相信大多数童鞋都遇见过；那么碰到这个问题，我们应该怎么办呢？在MySQL 5.7及之前版本，出现“too many connection”报错，超级用户root也无法登录上去，除了重启实例，没有其他更好的解决办法；不过在MySQL 8.0版本中，是对连接管理做了一些优化，下面我们就来看一下。

ERROR 1040 (HY000): Too many connections连接管理

在MySQL 8.0版本中，对连接管理这一块，是先后做了两个比较大的改变：一个是允许额外连接，另一个是专用的管理端口。

在MySQL 8.0版本中，在当前连接数达到最大连接数时，服务端允许1个额外连接，可以让具有CONNECTION_ADMIN权限的用户连接进来，下面简单测试一下。

（1）为了方便测试，先调整最大连接数

mysql> set global max_connections=3;Query OK, 0 rows affected (0.00 sec)

（2）多开几个会话，以达到最大连接数

mysql> show processlist;+----+-----------------+-----------------+------+---------+--------+------------------------+------------------+| Id | User | Host | db | Command | Time | State | Info |+----+-----------------+-----------------+------+---------+--------+------------------------+------------------+| 15 | event_scheduler | localhost | NULL | Daemon | 154190 | Waiting on empty queue | NULL || 54 | root | localhost | NULL | Query | 0 | starting | show processlist || 55 | test | 127.0.0.1:59120 | NULL | Sleep | 19 | | NULL || 56 | test | 127.0.0.1:59136 | NULL | Sleep | 9 | | NULL |+----+-----------------+-----------------+------+---------+--------+------------------------+------------------+4 rows in set (0.00 sec)mysql> show global status like ’threads_connected’;+-------------------+-------+| Variable_name | Value |+-------------------+-------+| Threads_connected | 3 |+-------------------+-------+4 rows in set (0.01 sec)

（3）普通用户test尝试连接，报错too many connections

$ mysql -utest -p -h127.0.0.1 -P10080Enter password: ERROR 1040 (08004): Too many connections

（4）超级用户root尝试连接成功

$ mysql -uroot -pEnter password: Welcome to the MySQL monitor. Commands end with ; or g.Your MySQL connection id is 60Server version: 8.0.20 MySQL Community Server - GPLCopyright (c) 2000, 2020, Oracle and/or its affiliates. All rights reserved.Oracle is a registered trademark of Oracle Corporation and/or itsaffiliates. Other names may be trademarks of their respectiveowners.Type ’help;’ or ’h’ for help. Type ’c’ to clear the current input statement.mysql>

（5）再次查看当前连接数，为max_connections+1

+----+-----------------+-----------------+------+---------+--------+------------------------+------------------+| Id | User | Host | db | Command | Time | State | Info |+----+-----------------+-----------------+------+---------+--------+------------------------+------------------+| 15 | event_scheduler | localhost | NULL | Daemon | 155064 | Waiting on empty queue | NULL || 54 | root | localhost | NULL | Query | 0 | starting | show processlist || 55 | test | 127.0.0.1:59120 | NULL | Sleep | 893 | | NULL || 56 | test | 127.0.0.1:59136 | NULL | Sleep | 883 | | NULL || 60 | root | localhost | NULL | Sleep | 141 | | NULL |+----+-----------------+-----------------+------+---------+--------+------------------------+------------------+5 rows in set (0.00 sec)mysql> show global status like ’threads_connected’;+-------------------+-------+| Variable_name | Value |+-------------------+-------+| Threads_connected | 4 |+-------------------+-------+4 rows in set (0.00 sec)

（6）超级用户root再次尝试连接，也报错too many connections

$ mysql -uroot -pEnter password: ERROR 1040 (HY000): Too many connections

通过上面测试可知，在MySQL 8.0中，允许的连接数为max_connections+1，其中这1个额外连接，只允许具有CONNECTION_ADMIN权限的用户使用。通过这1个额外连接，DBA可以使用超级用户root连接，进行kill会话等管理操作，以避免直接重启实例，降低成本，提高效率。

额外连接，在一定程度上，提供了出现too many connection问题时的临时解决手段，但额外数量只有1个，难免会有一些意外，出现类似'连接被抢用'、“终端异常掉线”等情况。因此，在MySQL 8.0.14版本中，又推出了一个非常重要的新特性——管理端口；它允许具有SERVICE_CONNECTION_ADMIN权限的用户，通过特定的IP和PORT连接上来，且没有连接数限制。

（1）先介绍下相关参数

admin_address：监听IP地址admin_port：监听端口create_admin_listener_thread：是否创建一个单独的线程来监听管理连接

（2）通过配置上述参数，即可启用管理端口

mysql> show global variables like ’admin%’;+---------------+-----------+| Variable_name | Value |+---------------+-----------+| admin_address | 127.0.0.1 || admin_port | 33062 |+---------------+-----------+2 rows in set (0.00 sec)# netstat -lntp | grep 33062tcp 0 0 127.0.0.1:33062 0.0.0.0:* LISTEN 20042/mysqld

（3）接下来进行测试

mysql> show processlist;+----+-----------------+-----------------+------+---------+--------+------------------------+------------------+| Id | User | Host | db | Command | Time | State | Info |+----+-----------------+-----------------+------+---------+--------+------------------------+------------------+| 15 | event_scheduler | localhost | NULL | Daemon | 168750 | Waiting on empty queue | NULL || 54 | root | localhost | NULL | Query | 0 | starting | show processlist || 55 | test | 127.0.0.1:59120 | NULL | Sleep | 14579 | | NULL || 56 | test | 127.0.0.1:59136 | NULL | Sleep | 14569 | | NULL |+----+-----------------+-----------------+------+---------+--------+------------------------+------------------+4 rows in set (0.00 sec)mysql> show global status like ’threads_connected’;+-------------------+-------+| Variable_name | Value |+-------------------+-------+| Threads_connected | 3 |+-------------------+-------+1 row in set (0.00 sec)

（4）普通用户test尝试连接，报错too many connections

$ mysql -utest -p -h127.0.0.1 -P10080Enter password: ERROR 1040 (08004): Too many connections

（5）超级用户root尝试通过管理端口连接成功

$ mysql -uroot -p -h127.0.0.1 -P33062Enter password: Welcome to the MySQL monitor. Commands end with ; or g.Your MySQL connection id is 62Server version: 8.0.20 MySQL Community Server - GPLCopyright (c) 2000, 2020, Oracle and/or its affiliates. All rights reserved.Oracle is a registered trademark of Oracle Corporation and/or itsaffiliates. Other names may be trademarks of their respectiveowners.Type ’help;’ or ’h’ for help. Type ’c’ to clear the current input statement.mysql>

（6）继续多开几个会话，使用超级用户root，通过管理端口连接成功，不受最大连接数max_connections限制

mysql> show processlist;+----+-----------------+-----------------+------+---------+--------+------------------------+------------------+| Id | User | Host | db | Command | Time | State | Info |+----+-----------------+-----------------+------+---------+--------+------------------------+------------------+| 15 | event_scheduler | localhost | NULL | Daemon | 169035 | Waiting on empty queue | NULL || 54 | root | localhost | NULL | Query | 0 | starting | show processlist || 55 | test | 127.0.0.1:59120 | NULL | Sleep | 14864 | | NULL || 56 | test | 127.0.0.1:59136 | NULL | Sleep | 14854 | | NULL || 62 | root | 127.0.0.1:47660 | NULL | Sleep | 151 | | NULL || 63 | root | 127.0.0.1:47760 | NULL | Sleep | 52 | | NULL || 64 | root | 127.0.0.1:47768 | NULL | Sleep | 43 | | NULL || 65 | root | 127.0.0.1:47780 | NULL | Sleep | 35 | | NULL || 66 | root | 127.0.0.1:47790 | NULL | Sleep | 24 | | NULL || 67 | root | 127.0.0.1:47800 | NULL | Sleep | 16 | | NULL || 68 | root | 127.0.0.1:47808 | NULL | Sleep | 8 | | NULL |+----+-----------------+-----------------+------+---------+--------+------------------------+------------------+11 rows in set (0.00 sec)mysql> show global status like ’threads_connected’;+-------------------+-------+| Variable_name | Value |+-------------------+-------+| Threads_connected | 10 |+-------------------+-------+1 row in set (0.00 sec)

可以说，有了管理端口这个新功能，DBA再也不用担心too many connections的问题。

在MySQL 8.0版本中，为了应对too many connections的场景，先后推出了额外连接和管理端口两个新功能，可以让DBA方便、快速地解决问题；不过，这始终是一个临时应急手段，最根本的原因还是要排查应用端的配置(并发限流、SQL性能、连接池配置等等)，以彻底规避此类问题。

以上就是MySQL 8.0新特性 — 管理端口的使用简介的详细内容，更多关于MySQL 8.0新特性 — 管理端口的资料请关注好吧啦网其它相关文章！