[GitHub] [arrow] lidavidm commented on pull request #9620: ARROW-11843: [C++] Provide reentrant Parquet reader

[GitBox]

lidavidm commented on pull request #9620:
URL: https://github.com/apache/arrow/pull/9620#issuecomment-814393897


   Properly implementing OpenAsync mostly fixes the discrepancy between 
prebuffer/no prebuffer on local files, so it seems most of the bottleneck there 
was just synchronously opening files.
   
   ![Local Median Scan Time 
(2)](https://user-images.githubusercontent.com/327919/113769583-2199a680-96ef-11eb-87d3-f7e52d8cbd93.png)
   ![S3 Median Scan Time 
(2)](https://user-images.githubusercontent.com/327919/113769586-22cad380-96ef-11eb-99e1-a302fa18c56a.png)
   


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