SHOW VARIABLES LIKE '%connection%';
character_set_connection utf8mb4
collation_connection utf8mb4_general_ci
extra_max_connections
max_connections 1250
max_user_connections 1250
https://dev.mysql.com/doc/refman/5.7/en/too-many-connections.html
支持的最大连接数为 max_connections +1
B.5.2.6 Too many connections
If you get a Too many connections error when you try to connect to the mysqld server, this means that all available connections are in use by other clients.
The number of connections permitted is controlled by the max_connections system variable. The default value is 151 to improve performance when MySQL is used with the Apache Web server. (Previously, the default was 100.) If you need to support more connections, you should set a larger value for this variable.
mysqld actually permits max_connections+1 clients to connect. The extra connection is reserved for use by accounts that have the SUPER privilege. By granting the SUPER privilege to administrators and not to normal users (who should not need it), an administrator who also has the PROCESS privilege can connect to the server and useSHOW PROCESSLIST to diagnose problems even if the maximum number of unprivileged clients are connected. SeeSection 13.7.5.29, “SHOW PROCESSLIST Syntax”.
The maximum number of connections MySQL supports depends on the quality of the thread library on a given platform, the amount of RAM available, how much RAM is used for each connection, the workload from each connection, and the desired response time. Linux or Solaris should be able to support at least 500 to 1000 simultaneous connections routinely and as many as 10,000 connections if you have many gigabytes of RAM available and the workload from each is low or the response time target undemanding. Windows is limited to (open tables × 2 + open connections) < 2048 due to the Posix compatibility layer used on that platform.
Increasing open-files-limit may be necessary. Also see Section 2.5, “Installing MySQL on Linux”, for how to raise the operating system limit on how many handles can be used by MySQL.