yingdachen commented on a change in pull request #37: TEZ-4042: Speculative
attempts should avoid running on the same node
URL: https://github.com/apache/tez/pull/37#discussion_r258660644
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File path: tez-dag/src/main/java/org/apache/tez/dag/app/dag/impl/TaskImpl.java
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@@ -1009,14 +1014,18 @@ public TaskStateInternal transition(TaskImpl task,
TaskEvent event) {
public void transition(TaskImpl task, TaskEvent event) {
LOG.info("Scheduling a redundant attempt for task " + task.taskId);
task.counters.findCounter(TaskCounter.NUM_SPECULATIONS).increment(1);
- TezTaskAttemptID earliestUnfinishedAttempt = null;
+ TaskAttempt earliestUnfinishedAttempt = null;
for (TaskAttempt ta : task.attempts.values()) {
// find the oldest running attempt
if (!ta.isFinished()) {
- earliestUnfinishedAttempt = ta.getID();
+ earliestUnfinishedAttempt = ta;
}
}
- task.addAndScheduleAttempt(earliestUnfinishedAttempt);
+ NodeId nodeId = earliestUnfinishedAttempt.getNodeId();
+ task.unhealthyNodesHistory.add(nodeId);
Review comment:
Indeed, the default speculator enforces that only one speculative attempt is
allowed today, but i would still think including all running nodes here would
be slightly better:
1. with only one speculation allowed, there can be one running attempts
above when we got here, so just adding its node to unhealthyNodeHistory is
equivalent to adding the earliestUnfinishedAttempt's node.
2. the fact that there can be only one speculative today, should be
orthogonal to our desire to avoid using the same (possibly problematic) nodes
for speculative attempt, therefore syntax wise, I think adding all running
nodes (at the time when we are adding additional speculative attempt) to
unhealthy history would make more sense, and it would be extensible too in the
future, if we decide that having more than one speculative should be allowed.
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