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https://issues.apache.org/jira/browse/HIVE-18608?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16349660#comment-16349660
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Mithun Radhakrishnan edited comment on HIVE-18608 at 2/2/18 2:03 AM:
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I've attached an initial implementation, where dictionary encoding might be
disabled via a table-property ({{'orc.skip.dictionary.for.columns'}}).
Note: I've only added support for top-level columns. Specifying this on a
{{STRUCT}} will disable dictionary encoding for the entire sub-tree (i.e. all
members of the STRUCT), recursively.
It might be good to support selection at an arbitrary depth, at a later date.
E.g. {{myInfoArray.__elem__.emailBody}}.
was (Author: mithun):
I've attached an initial implementation, where dictionary encoding might be
disabled via a table-property ({{'orc.skip.dictionary.for.columns'}}.
Note: I've only added support for top-level columns. Specifying this on a
{{STRUCT}} will disable dictionary encoding for the entire sub-tree (i.e. all
members of the STRUCT), recursively.
It might be good to support selection at an arbitrary depth, at a later date.
E.g. {{myInfoArray.__elem__.emailBody}}.
> ORC should allow selectively disabling dictionary-encoding on specified
> columns
> -------------------------------------------------------------------------------
>
> Key: HIVE-18608
> URL: https://issues.apache.org/jira/browse/HIVE-18608
> Project: Hive
> Issue Type: New Feature
> Components: ORC
> Affects Versions: 3.0.0, 2.4.0, 2.2.1
> Reporter: Mithun Radhakrishnan
> Assignee: Mithun Radhakrishnan
> Priority: Major
> Attachments: HIVE-18608.1-branch-2.2.patch
>
>
> Just as ORC allows the choice of columns to enable bloom-filters on, it would
> be nice to have a way to specify which columns {{DICTIONARY_V2}} encoding
> should be disabled on.
> Currently, the choice of dictionary-encoding depends on the results of
> sampling the first row-stride within a stripe. If the user knows that a
> column's cardinality is bound to prevent an effective dictionary, she might
> choose to simply disable it on just that column, and avoid the cost of
> sampling in the first row-stride.
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