Today we had a customer call in who had a problem with their magento site. What had happened was they had reached the maximum number of connections for their MySQL.

 250481 | someuser | localhost:7777 | somewebsite | Query   | 2464 | Writing to net               | SELECT /*!40001 SQL_NO_CACHE */ * FROM `mg_sales_flat_quote_address`                                 

| 250486 | someuser | localhost       | somewebsite | Query   | 2459 | Waiting for table level lock | INSERT INTO `mg_sales_flat_quote_address` (`quote_id`, `created_at`, `updated_at`, `customer_id`, `a |         0 |             0 |         0 |

.. and a whole load more waiting for table level lock were underneath

Solution is simple;

kill 250481

250481 is the processid of the select query causing these issues. I suspect it will go away, eventually but in the meantime, want to make sure the max connections don’t get reached, otherwise website will be down again!