mysql> show GLOBAL VARIABLES LIKE "max_%";
+----------------------------+----------------------+
| Variable_name              | Value                |
+----------------------------+----------------------+
| max_allowed_packet         | 16777216             |
| max_binlog_cache_size      | 18446744073709547520 |
| max_binlog_size            | 1073741824           |
| max_binlog_stmt_cache_size | 18446744073709547520 |
| max_connect_errors         | 10                   |
| max_connections            | 500                  |
| max_delayed_threads        | 20                   |
| max_error_count            | 64                   |
| max_heap_table_size        | 16777216             |
| max_insert_delayed_threads | 20                   |
| max_join_size              | 18446744073709551615 |
| max_length_for_sort_data   | 1024                 |
| max_long_data_size         | 16777216             |
| 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 |
+----------------------------+----------------------+

起動している間に、最高どこまでコネクションされたか。

mysql> show status like 'Max%';
+----------------------+-------+
| Variable_name        | Value |
+----------------------+-------+
| Max_used_connections | 186   |
+----------------------+-------+
1 row in set (0.01 sec)

現在のコネクション数。

mysql> show status like 'Threads_connected%';
+-------------------+-------+
| Variable_name     | Value |
+-------------------+-------+
| Threads_connected | 63    |
+-------------------+-------+
1 row in set (0.00 sec)

Apache側でエラーが出る。

# more /var/log/httpd/error_log
[Fri Feb 22 05:00:49 2013] [error] [client 111.111.111.111] PDO Connection Error: SQLSTATE[08004] [1040] Too many connections

mysql> set global max_connections=450;