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https://issues.apache.org/jira/browse/MAPREDUCE-1555?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12840751#action_12840751
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Arun C Murthy commented on MAPREDUCE-1555:
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Ruyue - this is poorly documented, but mostly right. If I remember right, this
was done so that the MapTask object in JobTracker doesn't have a reference to
the input-split. This will not cause a problem because a single MapTask object
on the JobTracker is never re-used i.e. a new one is created, serialized to the
TaskTracker during scheduling and it's splitMetaInfo is never needed again.
> Maybe some code of MapTask is wrong.
> ------------------------------------
>
> Key: MAPREDUCE-1555
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-1555
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Components: task
> Reporter: Ruyue Ma
>
> {code:title=MapTask.java|borderStyle=solid}
> public void write(DataOutput out) throws IOException {
> super.write(out);
> if (isMapOrReduce()) {
> splitMetaInfo.write(out);
> splitMetaInfo = null; // HERE: why set null ??????
> }
> }
> {code}
> In above code, if the splitMetaInfo is set null, Second Serialization (will
> invoke write) will throw NullPointerException.
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