[jira] [Commented] (HIVE-3874) Create a new Optimized Row Columnar file format for Hive

["Namit Jain (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HIVE-3874?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13548710#comment-13548710 ] 

Namit Jain commented on HIVE-3874:
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Owen, will it also be more compact overall ?
Will it be possible to perform dictionary encoding for a string ? Some initial experiments we performed on top of RCFile suggested that
dictionary encoding for low cardinality columns gives very good overall space savings for some of our top tables.

It would be useful to have a initial patch/doc out asap, so that we can also play around with it.
                
> 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
>
> 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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