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https://issues.apache.org/jira/browse/HADOOP-5553?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12689155#action_12689155
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Hong Tang commented on HADOOP-5553:
-----------------------------------
bq. Since SequenceFile provides a public methos nextRawValue(ValueBytes val),
which accpets a ValueBytes param. And also ValueBytes is a public interface. So
it seems it allows users to define their own ValueBytes implementations. But in
nextRawValue(ValueBytes val), it casts the passed param into either
CompressedBytes and UnCompressedBytes. I do not think it makes any sence.
I think the current interface is a good example of how to hide information
through the use of interface. The intention of this interface is to allow
people to pass value bytes to an outputstream when people do not need to
examine the deserialized object. In the meantime, it hides the implementation
detail that it is implemented by eagerly reading bytes into a byte array.
bq. Actually i am trying to skip some bytes of the value part of one record,
and not lazy load. Is there a possibility to allow SequenceFile to extend to
support this?
That is a valid concern, but have you profiled your code that skipping bytes is
indeed the right place you want to optimize for? Have you tried the alternative
of obtaining the serialized value bytes through a ByteArrayOutputStream, and
then do skipping from byte[]?
Finally, a different way of achieving this goal (accessing raw bytes in
read-only fashion without exposing implementation details) is to return an
InputStream for the value bytes. This is the approach taken by Hadoop-3315.
> Change modifier of SequenceFile.CompressedBytes and
> SequenceFile.UncompressedBytes from private to public
> ---------------------------------------------------------------------------------------------------------
>
> Key: HADOOP-5553
> URL: https://issues.apache.org/jira/browse/HADOOP-5553
> Project: Hadoop Core
> Issue Type: Improvement
> Reporter: He Yongqiang
> Attachments: Hadoop-5553-2.patch, Hadoop-5553-3.patch,
> Hadoop-5553.patch
>
>
> SequenceFile.rawValue() provides the only interface to navigate the
> underlying bytes. And with some little work on implementing a customized
> ValueBytes can avoid reading all bytes into memory. Unfortunately, the
> current nextRawValue will cast the passing ValueBytes to either private class
> CompressedBytes or private class UnCompressedBytes, this will disallow user
> further extension.
> I can not see any reason that CompressedBytes and UnCompressedBytes should be
> set to private. And since the ValueBytes is public and nextValue() casts it
> to either CompressedBytes or UnCompressedBytes, i think it would be better if
> they are public.
> I am stuck now by this issue, really appracited if this got resolved as soon
> as possible.
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