MySQL使用federated 实现Oacle链路效果

SHOW STATUS LIKE '%connect%';
Threads_connected is the current count, Max_used_connections is the highest value seen since the last time FLUSH STATUS was issued.

If that max value is the same as (or 1 more than) the value returned by SHOW VARIABLES LIKE 'max_connections'; then at some point that server was maxed out and could have returned this message.

If the remote server shows a lot of idle inbound federated connections, you may find that issuing FLUSH TABLES on the local server will release them.