为什么MySQL允许比max_connections限制更多的连接？

Question

这是我的连接数据。

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 |
+----------------------------+----------------------+

我想知道为什么允许比max_connections限制更多的连接？mysql不应该拒绝更多的连接，还是缓慢地修剪旧的连接？从日志中可以看出，后者是真的吗？

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)

这是否意味着，如果不再需要数据，那么关闭旧连接并不重要，因为mysql会慢慢地修剪这些连接吗？

Answer 1

我认为，查看同时处理了多少连接的参数是Max_used_connections。

自上次重新启动以来，Connections字段应该充当连接的计数器。

连接到MySQL服务器的连接尝试次数(成功与否)。Max_used_connections :自服务器启动以来同时使用的最大连接数。

您可以进一步参考这个SE回答和文献资料。

Answer 2

这不是活动连接的数量。Connections是连接尝试成功与否的次数。您需要查看Threads_connected号码。您还可以使用netstat和mysql端口上的过滤器检查连接。

这是类似的帖子来自stackoverlow。