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From "Dick King (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MAPREDUCE-15) SequenceFile RecordReader should skip bad records
Date Mon, 23 Aug 2010 16:58:19 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-15?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12901479#action_12901479

Dick King commented on MAPREDUCE-15:

Should the framework carry a {{mapreduce.max.corrupt.input.record.fraction}} and {{mapreduce.max.corrupt.input.record.excess}}

The framework catches and skips the corrupt records, and the bad and good record counts flow
back to the job tracker as counters, and if the number of bad records ever exceeds, {{...fraction
* number-of-good-records + ...excess}} the job is killed?

> SequenceFile RecordReader should skip bad records
> -------------------------------------------------
>                 Key: MAPREDUCE-15
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-15
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>            Reporter: Joydeep Sen Sarma
> Currently a bad record in a sequencefile leads to entire job being failed. the best workaround
is to skip an errant file manually (by looking at what map task failed).  This is a sucky
option because it's manual and because one should be able to skip a sequencefile block (instead
of entire file).
> While we don't see this often (and i don't know why this corruption happened) - here's
an example stack:
> Status : FAILED java.lang.NegativeArraySizeException
> 	at org.apache.hadoop.io.BytesWritable.setCapacity(BytesWritable.java:96)
> 	at org.apache.hadoop.io.BytesWritable.setSize(BytesWritable.java:75)
> 	at org.apache.hadoop.io.BytesWritable.readFields(BytesWritable.java:130)
> 	at org.apache.hadoop.io.SequenceFile$Reader.getCurrentValue(SequenceFile.java:1640)
> 	at org.apache.hadoop.io.SequenceFile$Reader.next(SequenceFile.java:1712)
> 	at org.apache.hadoop.mapred.SequenceFileRecordReader.next(SequenceFileRecordReader.java:79)
> 	at org.apache.hadoop.mapred.MapTask$1.next(MapTask.java:176)
> Ideally the recordreader should just skip the entire chunk if it gets an unrecoverable
error while reading.
> This was the consensus in hadoop-153 as well (that data corruptions should be handled
by recordreaders) and hadoop-3144 did something similar for textinputformat.

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