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https://issues.apache.org/jira/browse/HIVE-3874?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13561067#comment-13561067
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Alan Gates commented on HIVE-3874:
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bq. Letting new ORC format have some backward compatibility with RCFile will
save a lot of trouble.
[~he yongqiang], I'm curious what trouble this would solve. Hive handles the
case where different partitions in a table have different formats. Rather than
trying to integrate these two formats at the InputFormat/SerDe level it makes
more sense to me to test that when a table has some partitions in RC and some
in ORC reads across the partitions still works.
> 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, orc.tgz
>
>
> 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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