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https://issues.apache.org/jira/browse/IMPALA-4994?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16638316#comment-16638316
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Tim Armstrong commented on IMPALA-4994:
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I also messed around a little bit with this as part of IMPALA-4123. I've been
trying to add the missing tests to get that patch ready. I think the two
changes are independent but there would be code conflicts for sure.
> Push conversion and validation into dictionary construction
> -----------------------------------------------------------
>
> Key: IMPALA-4994
> URL: https://issues.apache.org/jira/browse/IMPALA-4994
> Project: IMPALA
> Issue Type: Improvement
> Components: Backend
> Affects Versions: Impala 2.9.0
> Reporter: Joe McDonnell
> Assignee: Csaba Ringhofer
> Priority: Major
> Labels: ramp-up
>
> Certain data types require conversion and/or validation when read from a
> Parquet file. For example, timestamps can require conversion to account for
> different storage offsets. Char/varchar fields can require conversion to
> handle lengths and space padding. Timestamps require validation, because not
> all bit combinations are valid timestamps.
> Right now, this is done per element as it is read. For dictionary encoded
> columns, it would save processing to do the conversion/validation once at
> dictionary construction.
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