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Posted to issues@arrow.apache.org by "Paddy Horan (Jira)" <ji...@apache.org> on 2020/05/23 11:30:00 UTC
[jira] [Updated] (ARROW-8902) [rust][datafusion] optimize count(*)
queries on parquet sources
[ https://issues.apache.org/jira/browse/ARROW-8902?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Paddy Horan updated ARROW-8902:
-------------------------------
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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