Why is MySQL allowing more connections than max_connections limit?

Here's my connection stats.

mysql> show status like 'Conn%';
+-----------------------------------+-------+
| Variable_name                     | Value |
+-----------------------------------+-------+
| 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                       | 274   |
+-----------------------------------+-------+

mysql> SHOW VARIABLES LIKE 'max_%';
+----------------------------+----------------------+
| Variable_name              | Value                |
+----------------------------+----------------------+
| max_allowed_packet         | 16777216             |
| max_binlog_cache_size      | 18446744073709547520 |
| max_binlog_size            | 104857600            |
| max_binlog_stmt_cache_size | 18446744073709547520 |
| max_connect_errors         | 100                  |
| max_connections            | 151                  |
| max_delayed_threads        | 20                   |
| max_digest_length          | 1024                 |
| max_error_count            | 64                   |
| max_execution_time         | 0                    |
| max_heap_table_size        | 16777216             |
| max_insert_delayed_threads | 20                   |
| max_join_size              | 18446744073709551615 |
| max_length_for_sort_data   | 1024                 |
| max_points_in_geometry     | 65536                |
| max_prepared_stmt_count    | 16382                |
| max_relay_log_size         | 0                    |
| max_seeks_for_key          | 18446744073709551615 |
| max_sort_length            | 1024                 |
| max_sp_recursion_depth     | 0                    |
| max_tmp_tables             | 32                   |
| max_user_connections       | 0                    |
| max_write_lock_count       | 18446744073709551615 |
+----------------------------+----------------------+

I'm wondering why more connections are being allowed than the max_connections limit? Shouldn't mysql refuse more connections or does it slowly prune old ones? From logs it appears that latter is true?

tail -f /var/log/mysql/error.log
2020-12-15T07:21:59.253969Z 60 [Note] Aborted connection 60 to db: 'my_db' user: 'my_user' host: 'my_ip' (Got an error reading communication packets)
2020-12-15T07:21:59.253979Z 57 [Note] Aborted connection 57 to db: 'my_db' user: 'my_user' host: 'my_ip' (Got an error reading communication packets)
2020-12-15T07:21:59.253994Z 56 [Note] Aborted connection 56 to db: 'my_db' user: 'my_user' host: 'my_ip' (Got an error reading communication packets)
2020-12-15T07:21:59.254119Z 58 [Note] Aborted connection 58 to db: 'my_db' user: 'my_user' host: 'my_ip' (Got an error reading communication packets)
2020-12-15T07:21:59.254136Z 54 [Note] Aborted connection 54 to db: 'my_db' user: 'my_user' host: 'my_ip' (Got an error reading communication packets)
2020-12-15T07:21:59.254143Z 59 [Note] Aborted connection 59 to db: 'my_db' user: 'my_user' host: 'my_ip' (Got an error reading communication packets)
2020-12-15T07:21:59.254154Z 61 [Note] Aborted connection 61 to db: 'my_db' user: 'my_user' host: 'my_ip' (Got an error reading communication packets)
2020-12-15T07:21:59.254565Z 55 [Note] Aborted connection 55 to db: 'my_db' user: 'my_user' host: 'my_ip' (Got an error reading communication packets)
2020-12-15T07:21:59.254581Z 53 [Note] Aborted connection 53 to db: 'my_db' user: 'my_user' host: 'my_ip' (Got an error reading communication packets)
2020-12-15T07:21:59.254593Z 62 [Note] Aborted connection 62 to db: 'my_db' user: 'my_user' host: 'my_ip' (Got an error reading communication packets)

Does this mean it doesn't matter about closing old connections if the data is no longer required as mysql will slowly prune these anyway?

Solution 1:

I think that the parameter you should look at to see how many connections were handled at the same time is Max_used_connections.

The Connections field should act as a counter of connections since the last restart.

Connections

The number of connection attempts (successful or not) to the MySQL server.

Max_used_connections

The maximum number of connections that have been in use simultaneously since the server started.

You can refer to this SE answer and the documentation to deep further.

Solution 2:

This is not the number of active connections. Connections is the number of connection attempts successful or not. You need to look at Threads_connected number. You can also check connections using netstat and filter on mysql port.

This is a similar post from stackoverlow.