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https://issues.apache.org/jira/browse/PARQUET-1324?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Wes McKinney updated PARQUET-1324:
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Fix Version/s: cpp-1.6.0
> [C++] Read Parquet dictionary encoded ColumnChunks directly into an Arrow
> DictionaryArray
> -----------------------------------------------------------------------------------------
>
> Key: PARQUET-1324
> URL: https://issues.apache.org/jira/browse/PARQUET-1324
> Project: Parquet
> Issue Type: Improvement
> Components: parquet-cpp
> Reporter: Stav Nir
> Priority: Major
> Fix For: cpp-1.6.0
>
>
> Dictionary data is very common in parquet, in the current implementation
> parquet-cpp decodes dictionary encoded data always before creating a plain
> arrow array. This process is wasteful since we could use arrow's
> DictionaryArray directly and achieve several benefits:
> # Smaller memory footprint - both in the decoding process and in the
> resulting arrow table - especially when the dict values are large
> # Better decoding performance - mostly as a result of the first bullet -
> less memory fetches and less allocations.
> I think those benefits could achieve significant improvements in runtime.
> My direction for the implementation is to read the indices (through the
> DictionaryDecoder, after the RLE decoding) and values separately into 2
> arrays and create a DictionaryArray using them.
> There are some questions to discuss:
> # Should this be the default behavior for dictionary encoded data
> # Should it be controlled with a parameter in the API
> # What should be the policy in case some of the chunks are dictionary
> encoded and some are not.
> I started implementing this but would like to hear your opinions.
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