Imran Rashid updated SPARK-23888:
    Component/s: Scheduler

> speculative task should not run on a given host where another attempt is 
> already running on
> -------------------------------------------------------------------------------------------
>                 Key: SPARK-23888
>                 URL: https://issues.apache.org/jira/browse/SPARK-23888
>             Project: Spark
>          Issue Type: Bug
>          Components: Scheduler, Spark Core
>    Affects Versions: 2.3.0
>            Reporter: wuyi
>            Priority: Major
>              Labels: speculation
>             Fix For: 2.3.0
> There's a bug in:
> {code:java}
> /** Check whether a task is currently running an attempt on a given host */
>  private def hasAttemptOnHost(taskIndex: Int, host: String): Boolean = {
>    taskAttempts(taskIndex).exists(_.host == host)
>  }
> {code}
> This will ignore hosts which have finished attempts, so we should check 
> whether the attempt is currently running on the given host. 
> And it is possible for a speculative task to run on a host where another 
> attempt failed here before.
> Assume we have only two machines: host1, host2.  We first run task0.0 on 
> host1. Then, due to  a long time waiting for task0.0, we launch a speculative 
> task0.1 on host2. And, task0.1 finally failed on host1, but it can not re-run 
> since there's already  a copy running on host2. After another long time, we 
> launch a new  speculative task0.2. And, now, we can run task0.2 on host1 
> again, since there's no more running attempt on host1.

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