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https://issues.apache.org/jira/browse/SPARK-22736?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Hyukjin Kwon updated SPARK-22736:
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Labels: bulk-closed (was: )
> Consider caching decoded dictionaries in VectorizedColumnReader
> ---------------------------------------------------------------
>
> Key: SPARK-22736
> URL: https://issues.apache.org/jira/browse/SPARK-22736
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 2.2.1
> Reporter: Henry Robinson
> Priority: Major
> Labels: bulk-closed
>
> {{VectorizedColumnReader.decodeDictionaryIds()}} calls
> {{dictionary.decodeToX}} for every dictionary ID encountered in a
> dict-encoded Parquet page.
> The whole idea of dictionary encoding is that a) values are repeated in a
> page and b) the dictionary only contains values that are in a page. So we
> should be able to save some decoding cost by decoding the entire dictionary
> page once, at the cost of using some memory (but theoretically we could
> discard the encoded dictionary, I think), and using the decoded dictionary to
> populate rows.
> This is particularly true for TIMESTAMP data, which after SPARK-12297, might
> have a timezone conversion as part of its decoding step.
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