MySQL 8.0 Release Notes
MySQL 8.0 Source Code Documentation
If clients encounter Too many connections
errors when attempting to connect to the
mysqld server, all available connections
are in use by other clients.
The permitted number of connections 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. To support more
connections, set
max_connections to a larger
value.
mysqld actually permits
max_connections
+ 1 client connections. The extra connection is reserved for
use by accounts that have the
CONNECTION_ADMIN or
SUPER privilege. By granting
the privilege to administrators and not to normal users (who
should not need it), an administrator can connect to the
server and use SHOW PROCESSLIST
to diagnose problems even if the maximum number of
unprivileged clients are connected. See
Section 13.7.7.29, “SHOW PROCESSLIST Statement”.
The server also permits administrative connections on a dedicated interface. For more information about how the server handles client connections, see Section 8.12.4.1, “How MySQL Handles Client Connections”.