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https://issues.apache.org/jira/browse/MAPREDUCE-2208?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13607966#comment-13607966
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Christian Tzolov commented on MAPREDUCE-2208:
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Ah, I've only looked at the CSVTextInputFormat, which doesn't override the
getSplits(). CSVNLineInputFormat does indeed.
So the CSVNLineInputFormat implementation reads the entire data set twice? Once
to compute the splits and second pass for the actual read in the map tasks.
While the double-passing approach is unavoidable (IMO) I wonder what is the
performance (and perhaps the scalability) impact. Do you have any numbers
comparing the standart vs. multiline implementations?
Thanks, Chris
> Flexible CSV text parser InputFormat
> ------------------------------------
>
> Key: MAPREDUCE-2208
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-2208
> Project: Hadoop Map/Reduce
> Issue Type: New Feature
> Reporter: Lance Norskog
> Priority: Trivial
> Attachments: CSVTextInputFormat.java, TestCSVTextFormat.java
>
>
> CSVTextInputFormat is a configurable CSV parser tuned to most of the
> csv-style datasets I've found. The Hadoop samples I've seen all
> FileInputFormat and Mapper<LongWritable,Text>. They drop the Longwritable key
> and parse the Text value as a CSV line. But, they are all custom-coded for
> the format.
> CSVTextInputFormat takes any csv-encoded file and rearrange the fields into
> the format required by a Mapper. You can drop fields & rearrange them. There
> is also a random sampling option to make training/test runs easier.
> Attached are CSVTextInputFormat.java and a unit test for it. Both go into
> org.apache.hadoop.mapreduce.lib.input under src/java and test/mapred/src.
> This is compiled against hadoop-0.0.20.
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