[jira] [Commented] (ARROW-13467) [C++] Support delta dictionaries in the IPC file format

["Ian Cook (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ARROW-13467?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17476403#comment-17476403 ] 

Ian Cook commented on ARROW-13467:
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See this thread from the user@ list for more details and notes on a possible resolution: https://lists.apache.org/thread/ygzc8gj5nv7453wwg4k0g0d9pl51qs2l

> [C++] Support delta dictionaries in the IPC file format
> -------------------------------------------------------
>
>                 Key: ARROW-13467
>                 URL: https://issues.apache.org/jira/browse/ARROW-13467
>             Project: Apache Arrow
>          Issue Type: Improvement
>          Components: C++
>            Reporter: Weston Pace
>            Priority: Major
>
> The spec states:
> > In the file format, there is no requirement that dictionary keys should be defined in a
> > {{DictionaryBatch}} before they are used in a {{RecordBatch}}, as long as the keys are
> > defined somewhere in the file. Further more, it is invalid to have more than one *non-delta*
> > dictionary batch per dictionary ID (i.e. dictionary replacement is not supported). Delta
> > dictionaries are applied in the order they appear in the file footer.
> This seems to suggest that dictionary deltas (but not replacements) are allowed.  However, both reading and writing an IPC file with a dictionary delta fails.



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