Major Description
We can reproduce the hung job by doing the following:
1. Run a sleep job with a concurrency of 1, speculation enabled, and 3 tasks
HADOOP_CLASSPATH="$TEZ_HOME/*:$TEZ_HOME/lib/*:$TEZ_CONF_DIR" yarn jar $TEZ_HOME/tez-tests-*.jar mrrsleep -Dtez.am.vertex.max-task-concurrency=1 -Dtez.am.speculation.enabled=true -Dtez.task.timeout-ms=60000 -m 3 -mt 60000 -ir 0 -irt 0 -r 0 -rt 0
2. Let the 1st task run to completion and then stop the 2nd task so that a speculative attempt is scheduled. Once the speculative attempt is scheduled for the 2nd task, continue the original attempt and let it complete.
kill -STOP <pid> // wait a few seconds for a speculative attempt to kick off kill -CONT <pid>
3. Kill the 3rd task, which will create a 2nd attempt
kill -9 <pid>
4. The next thing to be drawn off of the queue will be the speculative attempt of the 2nd task. However, it is already completed, so it will just sit in the final state and the job will hang.
Basically, for the failure to happen, the number of speculative tasks that are scheduled, but not yet ran has to be >= the concurrency of the job and there has to be at least 1 task failure.