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https://issues.apache.org/jira/browse/PARQUET-2149?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17541754#comment-17541754
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ASF GitHub Bot commented on PARQUET-2149:
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parthchandra commented on PR #968:
URL: https://github.com/apache/parquet-mr/pull/968#issuecomment-1136542868

   > So it sounds like you're optimizing one layer of processing, and I'm 
optimizing the next layer up, and it's kindof a coincidence that we're touching 
some of the same classes just because code reuse has been possible here.
   Yeah, kind of cool :)
   




> Implement async IO for Parquet file reader
> ------------------------------------------
>
>                 Key: PARQUET-2149
>                 URL: https://issues.apache.org/jira/browse/PARQUET-2149
>             Project: Parquet
>          Issue Type: Improvement
>          Components: parquet-mr
>            Reporter: Parth Chandra
>            Priority: Major
>
> ParquetFileReader's implementation has the following flow (simplified) - 
>       - For every column -> Read from storage in 8MB blocks -> Read all 
> uncompressed pages into output queue 
>       - From output queues -> (downstream ) decompression + decoding
> This flow is serialized, which means that downstream threads are blocked 
> until the data has been read. Because a large part of the time spent is 
> waiting for data from storage, threads are idle and CPU utilization is really 
> low.
> There is no reason why this cannot be made asynchronous _and_ parallel. So 
> For Column _i_ -> reading one chunk until end, from storage -> intermediate 
> output queue -> read one uncompressed page until end -> output queue -> 
> (downstream ) decompression + decoding
> Note that this can be made completely self contained in ParquetFileReader and 
> downstream implementations like Iceberg and Spark will automatically be able 
> to take advantage without code change as long as the ParquetFileReader apis 
> are not changed. 
> In past work with async io  [Drill - async page reader 
> |https://github.com/apache/drill/blob/master/exec/java-exec/src/main/java/org/apache/drill/exec/store/parquet/columnreaders/AsyncPageReader.java]
>  , I have seen 2x-3x improvement in reading speed for Parquet files.



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