Cause: Host becomes non-responsive Consequence: Unable to determine status of merge job Fix: Use generation Result: When host becomes non-responsive, engine attempts to fence the job, i.e. the host will fail to execute the job if attempts to. When trying to execute the job on a different host, there are two options: - Job completed on the previous host. This attempt fails (as expected) because the generation will be different on the engine and the host (generation on host incremented because the job successfully completed) - Job failed on the previous host. This attempt succeeds because generation on engine equals generation on the host