Zebing Lin created SPARK-30511:
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Summary: Spark marks ended speculative tasks as pending leads to
holding idle executors
Key: SPARK-30511
URL: https://issues.apache.org/jira/browse/SPARK-30511
Project: Spark
Issue Type: Bug
Components: Scheduler
Affects Versions: 2.3.0
Reporter: Zebing Lin
*TL;DR*
When speculative tasks finished/failed/got killed, they are still considered as
pending and count towards the calculation of number of needed executors.
h3. Symptom
In one of our production job (where it's running 4 tasks per executor), we
found that it was holding 6 executors at the end with only 2 tasks running (1
speculative). With more logging enabled, we found the job printed:
{code:java}
pendingTasks is 0 pendingSpeculativeTasks is 17 totalRunningTasks is 2
{code}
while the job only had 1 speculative task running and 16 speculative tasks
intentionally killed because of corresponding original tasks had finished.
h3. The Bug
Upon examining the code of _pendingSpeculativeTasks_:
{code:java}
stageAttemptToNumSpeculativeTasks.map { case (stageAttempt, numTasks) =>
numTasks -
stageAttemptToSpeculativeTaskIndices.get(stageAttempt).map(_.size).getOrElse(0)
}.sum
{code}
where _stageAttemptToNumSpeculativeTasks(stageAttempt)_ is incremented on
_onSpeculativeTaskSubmitted_, but never decremented.
_stageAttemptToNumSpeculativeTasks -= stageAttempt_ is performed on stage
completion. *This means Spark is marking ended speculative tasks as pending,
which leads to Spark to hold more executors that it actually needs!*
I will have a PR ready to fix this issue, along with SPARK-2840 too
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