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https://issues.apache.org/jira/browse/ARROW-5917?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Micah Kornfield resolved ARROW-5917.
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Fix Version/s: 0.15.0
Resolution: Fixed
Issue resolved by pull request 4994
[https://github.com/apache/arrow/pull/4994]
> [Java] Redesign the dictionary encoder
> --------------------------------------
>
> Key: ARROW-5917
> URL: https://issues.apache.org/jira/browse/ARROW-5917
> Project: Apache Arrow
> Issue Type: New Feature
> Components: Java
> Reporter: Liya Fan
> Assignee: Liya Fan
> Priority: Major
> Labels: pull-request-available
> Fix For: 0.15.0
>
> Time Spent: 12h 20m
> Remaining Estimate: 0h
>
> The current dictionary encoder implementation
> (org.apache.arrow.vector.dictionary.DictionaryEncoder) has heavy performance
> overhead, which prevents it from being useful in practice:
> # There are repeated conversions between Java objects and bytes (e.g.
> vector.getObject(i)).
> # Unnecessary memory copy (the vector data must be copied to the hash table).
> # The hash table cannot be reused for encoding multiple vectors (other data
> structure & results cannot be reused either).
> # The output vector should not be created/managed by the encoder (just like
> in the out-of-place sorter)
> # The hash table requires that the hashCode & equals methods be implemented
> appropriately, but this is not guaranteed.
> We plan to implement a new one in the algorithm module, and gradually
> deprecate the current one.
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