[jira] [Commented] (ARROW-3144) [C++] Better solution for cases where dictionaries are unknown at schema reconstruction time, or for delta dictionaries

["Wes McKinney (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ARROW-3144?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16782948#comment-16782948 ] 

Wes McKinney commented on ARROW-3144:
-------------------------------------

I suggest we handle dictionaries in Flight in the 0.14 release cycle

> [C++] Better solution for cases where dictionaries are unknown at schema reconstruction time, or for delta dictionaries
> -----------------------------------------------------------------------------------------------------------------------
>
>                 Key: ARROW-3144
>                 URL: https://issues.apache.org/jira/browse/ARROW-3144
>             Project: Apache Arrow
>          Issue Type: Improvement
>          Components: C++
>            Reporter: Wes McKinney
>            Priority: Major
>             Fix For: 0.14.0
>
>
> There are a couple of inter-related issues:
> * Cases where a system might send the schema without the dictionaries, and the user wishes to reason about the schema and its types without knowing the dictionary values
> * Dictionaries that are changing, e.g. using delta dictionary messages
> {{arrow::DictionaryType}} has no "linkage" to any external object. I propose adding a "LinkedDictionaryType" or something similar (purely a C++ construct), which functionally would be a subclass of {{DictionaryType}}, which would allow a type to be created which will obtain its dictionary later through some kind of "Dictionary provider" interface. There is something similar in Java already. This would allow a dictionary to evolve via delta dictionaries, or for a dictionary to be retrieved later e.g. through an RPC or IPC layer



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