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Posted to dev@arrow.apache.org by "Alex Gaynor (Jira)" <ji...@apache.org> on 2020/05/23 00:03:00 UTC

[jira] [Created] (ARROW-8902) [rust][datafusion] optimize count(*) queries on parquet sources

Alex Gaynor created ARROW-8902:
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             Summary: [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: Bug
          Components: Rust - DataFusion
            Reporter: Alex Gaynor


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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