To reproduce:

Import and configure a MySQL DB in HQ
Wait until all schema and tables are auto discovered and collecting in HQ
Shutdown MySQL database
Agent log is flooded with connection refused exceptions:

Last packet sent to the server was 0 ms ago.
2008-08-28 17:53:14,859 ERROR [ScheduleThread] [ScheduleThread] Metric Value not found: Query failed for Questions, while attempting to issue query SHOW /*!50002 GLOBAL */ STATUS LIKE 'Questions':Communications link failure due to underlying exception:

** BEGIN NESTED EXCEPTION **

java.net.ConnectException
MESSAGE: Connection refused: connect

STACKTRACE:

java.net.ConnectException: Connection refused: connect
        at java.net.PlainSocketImpl.socketConnect(Native Method)
        at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:333)
        at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:195)
        at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:182)
        at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366)
        at java.net.Socket.connect(Socket.java:520)
        at java.net.Socket.connect(Socket.java:470)
        at java.net.Socket.<init>(Socket.java:367)
        at java.net.Socket.<init>(Socket.java:209)
        at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:173)
        at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:267)
        at com.mysql.jdbc.Connection.createNewIO(Connection.java:2739)
        at com.mysql.jdbc.Connection.<init>(Connection.java:1553)
        at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:266)
        at java.sql.DriverManager.getConnection(DriverManager.java:525)
        at java.sql.DriverManager.getConnection(DriverManager.java:171)
        at org.hyperic.hq.plugin.mysql.MySQLMeasurementPlugin.getConnection(MySQLMeasurementPlugin.java:75)
        at org.hyperic.hq.product.JDBCMeasurementPlugin.getCachedConnection(JDBCMeasurementPlugin.java:196)
        at org.hyperic.hq.product.JDBCMeasurementPlugin.getQueryValue(JDBCMeasurementPlugin.java:246)
        at org.hyperic.hq.plugin.mysql.MySQLMeasurementPlugin.getQueryValue(MySQLMeasurementPlugin.java:230)
        at org.hyperic.hq.product.JDBCMeasurementPlugin.getValue(JDBCMeasurementPlugin.java:135)
        at org.hyperic.hq.plugin.mysql.MySQLMeasurementPlugin.getValue(MySQLMeasurementPlugin.java:141)
        at org.hyperic.hq.product.MeasurementPluginManager.getPluginValue(MeasurementPluginManager.java:176)
        at org.hyperic.hq.product.MeasurementPluginManager.getValue(MeasurementPluginManager.java:228)
        at org.hyperic.hq.measurement.agent.server.ScheduleThread.getValue(ScheduleThread.java:322)
        at org.hyperic.hq.measurement.agent.server.ScheduleThread.run(ScheduleThread.java:473)
        at java.lang.Thread.run(Thread.java:595)


** END NESTED EXCEPTION **