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https://issues.apache.org/jira/browse/MAPREDUCE-6166?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14226745#comment-14226745
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Eric Payne commented on MAPREDUCE-6166:
---------------------------------------
[~jira.shegalov], I have one question about re-using the {{input.read}} code in
{{OnDisMapOutput}}.
{quote}
We can set
{code}
long bytesLeft = compressedLength - ((IFileInputStream)input).getSize()
{code}
Then we don't need to touch the line {{input.read}} to do {{readWithChecksum}}
{quote}
In this case, {{input.read}} does not write the checksum to the disk while
{{readWithChecksum}} will write it.
Since {{OnDiskMapOutput}} is shuffling the whole IFile to disk, the checksum is
needed later during the last merge pass when the IFile contents are read again
and decompressed.
If we were to implement {{input.read}} as above, it looks like we would still
need to add something like the following in order to put the checksum on the
disk:
{code}
disk.write(((IFileInputStream)input).getChecksum(), 0, (int)
((IFileInputStream)input).getSize());
{code}
> Reducers do not catch bad map output transfers during shuffle if data
> shuffled directly to disk
> -----------------------------------------------------------------------------------------------
>
> Key: MAPREDUCE-6166
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-6166
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Components: mrv2
> Affects Versions: 2.6.0
> Reporter: Eric Payne
> Assignee: Eric Payne
> Attachments: MAPREDUCE-6166.v1.201411221941.txt,
> MAPREDUCE-6166.v2.201411251627.txt
>
>
> In very large map/reduce jobs (50000 maps, 2500 reducers), the intermediate
> map partition output gets corrupted on disk on the map side. If this
> corrupted map output is too large to shuffle in memory, the reducer streams
> it to disk without validating the checksum. In jobs this large, it could take
> hours before the reducer finally tries to read the corrupted file and fails.
> Since retries of the failed reduce attempt will also take hours, this delay
> in discovering the failure is multiplied greatly.
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