Sital Kedia created SPARK-13279:
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Summary: Spark driver stuck holding a global lock when there are
200k tasks submitted in a stage
Key: SPARK-13279
URL: https://issues.apache.org/jira/browse/SPARK-13279
Project: Spark
Issue Type: Bug
Components: Spark Core
Affects Versions: 1.6.0
Reporter: Sital Kedia
Fix For: 1.6.0
While running a large pipeline with 200k tasks, we found that the executors
were not able to register with the driver because the driver was stuck holding
a global lock in TaskSchedulerImpl.submitTasks function.
jstack of the driver - http://pastebin.com/m8CP6VMv
executor log - http://pastebin.com/2NPS1mXC
>From the jstack I see that the thread handing the resource offer from
>executors (dispatcher-event-loop-9) is blocked on a lock held by the thread
>"dag-scheduler-event-loop" which is iterating over an entire ArrayBuffer when
>adding a pending tasks. So when we have 200k pending tasks, because of this
>o(n2) operations, the driver is just hung for more than 5 minutes.
Solution - Instead of an ArrayBuffer, we can use a LinkedHashSet which will
provide us o(1) lookup and also maintain the ordering.
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