[jira] [Resolved] (ARROW-5917) [Java] Redesign the dictionary encoder

["Micah Kornfield (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/ARROW-5917?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Micah Kornfield resolved ARROW-5917.
------------------------------------
    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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