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From "Pete Wyckoff (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4065) support for reading binary data from flat files
Date Thu, 18 Sep 2008 17:44:44 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4065?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12632309#action_12632309

Pete Wyckoff commented on HADOOP-4065:

bq. Could the types be called FlatFileInputFormat and FlatFileRecordReader?
Yes, better names.

bq. Is a SerializationContext class needed?

If the Serialization is in contrib, one would need to use ReflectionUtils to instantiate it
and it wouldn't be in any Factory, would it?  So, in this case, it needs to know the name
of the Class to instantiate it, no?  

bq. an't just get these two classes from the Configuration itself.

wanted to make it extensible so it could some from the configuration or maybe some place else
- the name of the file or some external store or something depending on the application. Of
course, in that case, one could argue a higher level is setting that up anyway, so why don't
they just do the lookup and store the info in the configuration. 

bq. Shouldn't keys be file offsets, similar to TextInputFormat? The row numbers you have are
actually the row number within the split, which might be confusing (and they're not unique
per file).

Are the file offsets useful anywhere?  Maybe we should just always return the same instance
of some dummy Writable for performance if the key isn't used anyway??

> support for reading binary data from flat files
> -----------------------------------------------
>                 Key: HADOOP-4065
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4065
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: mapred
>            Reporter: Joydeep Sen Sarma
>         Attachments: FlatFileReader.java, HADOOP-4065.0.txt, HADOOP-4065.1.txt, HADOOP-4065.1.txt,
> like textinputformat - looking for a concrete implementation to read binary records from
a flat file (that may be compressed).
> it's assumed that hadoop can't split such a file. so the inputformat can set splittable
to false.
> tricky aspects are:
> - how to know what class the file contains (has to be in a configuration somewhere).
> - how to determine EOF (would be nice if hadoop can determine EOF and not have the deserializer
throw an exception  (which is hard to distinguish from a exception due to corruptions?)).
this is easy for non-compressed streams - for compressed streams - DecompressorStream has
a useful looking getAvailable() call - except the class is marked package private.

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