HAProxy, client timeouts when connecting from JDBC pool

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http://serverfault.com – I have a webapp (Tomcat/Hibernate/DBCP 1.4) that runs queries against MySQL, and this works fine for a certain load, say 50 queries a second. When I route the same moderate load through HAProxy (still just using a single database), I get a failure, maybe one for every 500 queries. My app reports: Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure The last packet successfully received from the server was 196,898 milliseconds ago. The last packet sent successfully to the server was 0 milliseconds ago. at sun.reflect.GeneratedConstructorAccessor21 (HowTos)