A poison message is a message containing information that an application cannot successfully process. A poison message is not a corrupt message, and may not be an invalid request. Service Broker contains message integrity checks that detect corrupt messages. An application also typically validates the content of a message, and discards a message that contains an illegal request. In contrast, many poison messages were valid when the message was created, but later became impossible to process.

Hash Warning events are fired when a hash recursion or hash bailout has occurred during a hashing operation. Both of these situations are less than desirable, as they mean that a Hash Join or Hash Aggregate has run out of memory and been forced to spill information to disk during query execution. When a hashing operation spills to disk, this almost always results in slower query performance and can cause space consumption increase in tempdb.