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https://issues.apache.org/jira/browse/HIVE-3874?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13549774#comment-13549774
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Owen O'Malley commented on HIVE-3874:
-------------------------------------
He Yongqiang, the APIs to the two formats are significantly different. It would
be possible to extend the RCFile reader to recognize an ORC file and to have it
delegate to the ORC File reader.
The other direction (having the ORC file reader parse an RCFile) isn't
possible, because ORC provides operations that would be very expensive or
impossible to implement in RCFile.
One concern with making the RCFile reader delegate to the ORC file reader is
that RCFile returns binary values that are interpreted by the serde while in
ORC deserialization happens in the reader. Therefore, either the adaptor would
need to re-serialize the data or would require changes in the serde as well.
> Create a new Optimized Row Columnar file format for Hive
> --------------------------------------------------------
>
> Key: HIVE-3874
> URL: https://issues.apache.org/jira/browse/HIVE-3874
> Project: Hive
> Issue Type: Improvement
> Components: Serializers/Deserializers
> Reporter: Owen O'Malley
> Assignee: Owen O'Malley
> Attachments: OrcFileIntro.pptx
>
>
> There are several limitations of the current RC File format that I'd like to
> address by creating a new format:
> * each column value is stored as a binary blob, which means:
> ** the entire column value must be read, decompressed, and deserialized
> ** the file format can't use smarter type-specific compression
> ** push down filters can't be evaluated
> * the start of each row group needs to be found by scanning
> * user metadata can only be added to the file when the file is created
> * the file doesn't store the number of rows per a file or row group
> * there is no mechanism for seeking to a particular row number, which is
> required for external indexes.
> * there is no mechanism for storing light weight indexes within the file to
> enable push-down filters to skip entire row groups.
> * the type of the rows aren't stored in the file
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