查看连接数问题

查看执行中的进程

SHOW FULL PROCESSLIST;
show processlist;

查看最大连接数

show variables like '%max_connections%';

8.0 中设置最大连接数

set persist max_connections=200;

锁问题查询

查看哪些表正在被使用当中

show OPEN TABLES where In_use > 0;

查看当前运行的所有事务

select * from information_schema.innodb_trx

查看锁的情况

mysql> show status like 'innodb_row_lock_%';
+-------------------------------+--------+
| Variable_name                 | Value  |
+-------------------------------+--------+
| Innodb_row_lock_current_waits | 1      |
| Innodb_row_lock_time          | 479764 |
| Innodb_row_lock_time_avg      | 39980  |
| Innodb_row_lock_time_max      | 51021  |
| Innodb_row_lock_waits         | 12     |
+-------------------------------+--------+
5 rows in set (0.00 sec)

解释如下：
Innodb_row_lock_current_waits : 当前等待锁的数量
Innodb_row_lock_time : 系统启动到现在，锁定的总时间长度
Innodb_row_lock_time_avg : 每次平均锁定的时间
Innodb_row_lock_time_max : 最长一次锁定时间
Innodb_row_lock_waits : 系统启动到现在总共锁定的次数