Ultra Pipeline Reprocess Feature

How will the ultra pipeline reprocess a failed message? It seems like all ultra pipeline has inbuilt reprocess mechanism in case of exceptions.
Wanted to know what could be the failure scenarios.

Thanks.

An Ultra Pipeline with unlinked input/outputs will receive requests for processing from the Feed-Masters in the Snaplex. The requests are stored in queues on the Feed-Masters until they are processed by the Ultra pipeline executions. If an execution fails while processing a request, possibly because a snap fails or if the node the execution is running on crashes, another execution will try to process the request. A request will be retried 5 times before the request is considered to be a “poison pill” and is dropped. (The request is dropped to ensure that it does not block other requests from being processed.)

As to what kind of failures there can be, the error views are automatically added to snaps in an Ultra execution, so it depends on the type of snap and error as to whether it will fail the pipeline versus writing to the error view.