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is the default port used by the "Admin interface".Through this interface you can configure ProxySQL and get metrics from it by using a normal MySQL client.

In order to connect to MySQL servers through ProxySQL you should connect to Port 6033 (by default).

for configuration check out also:

check out also:https://github.com/sysown/proxysql/wiki/ProxySQL-Configuration#mysql-query-rules

Yes, by default, it is possible that the requests coming from a single connection are evenly distributed among all the backends of the same hostgroup.