I'm Getting MySql max_connect_error, but Max_used_connections shows it didn't reach the limit

Question

From time to time, I'm getting an error "mysqli_connect(): (HY000/1203): User already has more than 'max_user_connections' active connections." I checked the MySQL max_connection variable, and it's at 150. What's odd is that when I check for Max_used_connections, it says 41, which (I think) implies that MySql never reached 150 simultaneous connections. The per-user Max_user_connections variable is 0, so it should effectively be the same as max_connections. Am I misunderstanding what these variables mean, or is something odd going on with MySql?

I use PHP to connect to MySql. The MySql version is 5.7.40

Here are the results of show status like '%connec%'; and show variables like '%connections%';

| Variable_name                                 | Value               |
+-----------------------------------------------+---------------------+
| Aborted_connects                              | 776                 |
| Connection_errors_accept                      | 0                   |
| Connection_errors_internal                    | 0                   |
| Connection_errors_max_connections             | 0                   |
| Connection_errors_peer_address                | 0                   |
| Connection_errors_select                      | 0                   |
| Connection_errors_tcpwrap                     | 0                   |
| Connections                                   | 8899838             |
| Locked_connects                               | 0                   |
| Max_used_connections                          | 41                  |
| Max_used_connections_time                     | 2022-10-25 13:57:07 |
| Performance_schema_session_connect_attrs_lost | 0                   |
| Ssl_client_connects                           | 0                   |
| Ssl_connect_renegotiates                      | 0                   |
| Ssl_finished_connects                         | 0                   |
| Threads_connected                             | 1                   |
+-----------------------------------------------+---------------------+

+----------------------+------------+
| Variable_name        | Value      |
+----------------------+------------+
| max_connections      | 150        |
| max_user_connections | 2147483647 |
+----------------------+------------+

Also, I doubt I'm using up all connections by serving web pages; I'm not doing complicated queries, and the data sets are relatively small. Can someone point me to how to find what process/user maxes out these resources?

Answer 1

Max_used_connections is a "high water mark".

max_user_connections -- Maximum simultaneous connections permitted for each user account. There are exceptions, such as for 'root' and when the value is 0.

If the user account has a nonzero MAX_USER_CONNECTIONS resource limit, the session max_user_connections value is set to that limit. -- Check this value, too. SHOW CREATE USER "..."@"...";

A typical PHP application will [or at least should] use at most 1 connection per web page, but a user can run through lots of pages rather fast. While they are flipping through pages, the "used" connections is going up and down by one. That one user is not contributing more than 1 to the "used". Meanwhile, a hidden counter is rapidly increasing toward his max_user_connections.

If "everyone" has the same login, then "user" is somewhat meaningless. More likely, the user connects to a web page, then then uses some common db connection. That is, all users end up incrementing the counter for that one login name.