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https://issues.apache.org/jira/browse/ARROW-8902?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Paddy Horan updated ARROW-8902:
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Issue Type: Improvement (was: Bug)
> [rust][datafusion] optimize count(*) queries on parquet sources
> ---------------------------------------------------------------
>
> Key: ARROW-8902
> URL: https://issues.apache.org/jira/browse/ARROW-8902
> Project: Apache Arrow
> Issue Type: Improvement
> Components: Rust - DataFusion
> Reporter: Alex Gaynor
> Priority: Minor
>
> Currently, as far as I can tell, when you perform a `select count(*) from
> dataset` in datafusion against a parquet dataset, the way this is implemented
> is by doing a scan on column 0, and counting up all of the rows (specifically
> I think it counts the # of rows in each batch).
>
> However, for the specific case of just counting _everythign_ in a parquet
> file, you can just read the rowcount from the footer metadata, so it's O(1)
> instead of O(n)
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