FAQ
Tasks are not scheduled even though task trackers have extra slots
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Key: HADOOP-5289
URL: https://issues.apache.org/jira/browse/HADOOP-5289
Project: Hadoop Core
Issue Type: Bug
Components: mapred
Affects Versions: 0.19.0
Reporter: Runping Qi



I ran a job with 51 reduce tasks on a cluster with 13 task trackers running Hadoop 0.19. Each task tracker has 5 reduce slots.
Initially, each task tracker accepted 4 reduce tasks as expected. However, 3 task trackers were put into blacklist because many tasks failed on them.
However, those failed tasks stayed in pending state, not being scheduled to other task trackers, even though each of the other healthy tracker has one free slot.


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  • Runping Qi (JIRA) at Feb 19, 2009 at 8:02 pm
    [ https://issues.apache.org/jira/browse/HADOOP-5289?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12675111#action_12675111 ]

    Runping Qi commented on HADOOP-5289:
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    Another aspect of this issue.
    Task failed on those 3 trackers because they have too little memory.
    Hadoop scheduler correctly detected that fact, and correctly determined that each of those trackers has the capacity of one slot.
    Thus, the cluster has the total capacity of 53 closts (10 * 5 + 3 * 1).
    However, the scheduler did not use that information when computing the maximum number of tasks each tracker can take for the job, and thought each task tracker should take 4 tasks, regardless of their actual capacity.


    Tasks are not scheduled even though task trackers have extra slots
    ------------------------------------------------------------------

    Key: HADOOP-5289
    URL: https://issues.apache.org/jira/browse/HADOOP-5289
    Project: Hadoop Core
    Issue Type: Bug
    Components: mapred
    Affects Versions: 0.19.0
    Reporter: Runping Qi

    I ran a job with 51 reduce tasks on a cluster with 13 task trackers running Hadoop 0.19. Each task tracker has 5 reduce slots.
    Initially, each task tracker accepted 4 reduce tasks as expected. However, 3 task trackers were put into blacklist because many tasks failed on them.
    However, those failed tasks stayed in pending state, not being scheduled to other task trackers, even though each of the other healthy tracker has one free slot.
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  • Devaraj Das (JIRA) at Feb 20, 2009 at 4:04 am
    [ https://issues.apache.org/jira/browse/HADOOP-5289?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12675230#action_12675230 ]

    Devaraj Das commented on HADOOP-5289:
    -------------------------------------

    Runping, did the pending tasks finally run when the other reducers completed or they remained in the PENDING state for ever ?
    Tasks are not scheduled even though task trackers have extra slots
    ------------------------------------------------------------------

    Key: HADOOP-5289
    URL: https://issues.apache.org/jira/browse/HADOOP-5289
    Project: Hadoop Core
    Issue Type: Bug
    Components: mapred
    Affects Versions: 0.19.0
    Reporter: Runping Qi

    I ran a job with 51 reduce tasks on a cluster with 13 task trackers running Hadoop 0.19. Each task tracker has 5 reduce slots.
    Initially, each task tracker accepted 4 reduce tasks as expected. However, 3 task trackers were put into blacklist because many tasks failed on them.
    However, those failed tasks stayed in pending state, not being scheduled to other task trackers, even though each of the other healthy tracker has one free slot.
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    This message is automatically generated by JIRA.
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  • Runping Qi (JIRA) at Feb 20, 2009 at 4:40 am
    [ https://issues.apache.org/jira/browse/HADOOP-5289?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12675239#action_12675239 ]

    Runping Qi commented on HADOOP-5289:
    ------------------------------------


    the pending tasks finally got scheduled.
    Tasks are not scheduled even though task trackers have extra slots
    ------------------------------------------------------------------

    Key: HADOOP-5289
    URL: https://issues.apache.org/jira/browse/HADOOP-5289
    Project: Hadoop Core
    Issue Type: Bug
    Components: mapred
    Affects Versions: 0.19.0
    Reporter: Runping Qi

    I ran a job with 51 reduce tasks on a cluster with 13 task trackers running Hadoop 0.19. Each task tracker has 5 reduce slots.
    Initially, each task tracker accepted 4 reduce tasks as expected. However, 3 task trackers were put into blacklist because many tasks failed on them.
    However, those failed tasks stayed in pending state, not being scheduled to other task trackers, even though each of the other healthy tracker has one free slot.
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    This message is automatically generated by JIRA.
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postedFeb 19, '09 at 7:46p
activeFeb 20, '09 at 4:40a
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