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Harden runaway split detection #13262

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losipiuk wants to merge 2 commits into from
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Harden runaway split detection #13262

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5684f90
Make thread name for split runner threads depend on time
losipiuk Jul 20, 2022
d55973a
Harden runaway split detection
losipiuk Jul 20, 2022
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9 changes: 8 additions & 1 deletion core/trino-main/src/main/java/io/trino/execution/SqlTaskManager.java
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Original file line number Diff line number Diff line change
Expand Up @@ -735,7 +735,14 @@ private void failStuckSplitTasks()
log.warn("%s is long running with stackTrace:\n%s", splitInfo.getSplitInfo(), stackTraceElements.stream().map(Object::toString).collect(joining(lineSeparator())));
}

return stuckSplitStackTracePredicate.test(stackTraceElements);
boolean isThreadStack = stuckSplitStackTracePredicate.test(stackTraceElements);

// We check if thread's name matches threadId stored in RunningSplitInfo to be sure that stacktrace we obtained belongs to the execution of split
// described by RunningSplitInfo.
// There is still a chance that we may observe the stacktrace from execution of new split before thread name is set in io.trino.execution.executor.TaskExecutor.TaskRunner.run()
// Yet, we assume that such stacktrace would not be classified as "stack" by stuckSplitStackTracePredicate.
boolean splitAssignmentDidNotChange = splitInfo.getThread().getName().startsWith(splitInfo.getThreadId());
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@martint martint Jul 20, 2022

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Relying on thread names is very brittle. There's no contract for thread names, no guarantee they are going to be the same or different for a given set of conditions, etc.

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@martint martint Jul 20, 2022

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There are other possible ways to do this. Some random ideas:

  • Create our own version of Thread that contains additional information that we can inspect
  • Drive the process of finding stuck threads from the list of all running splits instead of trying to infer the split by inspecting the threads
  • Maintain an external mapping of split <-> thread

Also, for any approach that relies on looking at the thread and then checking if it corresponds to the split we want to kill, there will always be a small window for a race condition unless we force proper synchronization of these checks with split-to-thread assignments.

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@losipiuk losipiuk Jul 21, 2022

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Yeah. I agree this is somewhat brittle. For my defence - there is test which (at least partially) verifies it works ;).
The simple change to that, keeping the same solution principle, would be to have thread <-> split-execution-id mapping, where split-execution-id would be incremented any time split assigned to a thread changes.

And yeah - there is a race-condition window still - I mention that in the comment.

return isThreadStack && splitAssignmentDidNotChange;
});

for (TaskId stuckSplitTaskId : stuckSplitTaskIds) {
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2 changes: 1 addition & 1 deletion core/trino-main/src/main/java/io/trino/execution/executor/TaskExecutor.java
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Expand Up @@ -479,7 +479,7 @@ public void run()
return;
}

String threadId = split.getTaskHandle().getTaskId() + "-" + split.getSplitId();
String threadId = split.getTaskHandle().getTaskId() + "-" + split.getSplitId() + "-" + System.nanoTime();
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@martint martint Jul 20, 2022

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This may negatively impact tools that gather thread dumps and attempt to group threads by name for analysis purposes.

try (SetThreadName splitName = new SetThreadName(threadId)) {
RunningSplitInfo splitInfo = new RunningSplitInfo(ticker.read(), threadId, Thread.currentThread(), split);
runningSplitInfos.add(splitInfo);
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