[jira] [Created] (PARQUET-1641) Parquet pages for different columns cannot be read in parallel

["Samarth Jain (Jira)" <ji...@apache.org>]

Samarth Jain created PARQUET-1641:
-------------------------------------

             Summary: Parquet pages for different columns cannot be read in parallel 
                 Key: PARQUET-1641
                 URL: https://issues.apache.org/jira/browse/PARQUET-1641
             Project: Parquet
          Issue Type: Improvement
            Reporter: Samarth Jain


All ColumnChunkPageReader instances use the same decompressor. 

[https://github.com/apache/parquet-mr/blob/master/parquet-hadoop/src/main/java/org/apache/parquet/hadoop/ParquetFileReader.java#L1286]

<code>

BytesInputDecompressor decompressor = options.getCodecFactory().getDecompressor(descriptor.metadata.getCodec());

return new ColumnChunkPageReader(decompressor, pagesInChunk, dictionaryPage);

</code>

 

The CodecFactory caches the decompressors for every codec type returning the same instance on every getCompressor(codecName) call. See the caching happening here:

[https://github.com/apache/parquet-mr/blob/master/parquet-hadoop/src/main/java/org/apache/parquet/hadoop/CodecFactory.java#L197]

<code>

@Override
public BytesDecompressor getDecompressor(CompressionCodecName codecName) {
 BytesDecompressor decomp = decompressors.get(codecName);
 if (decomp == null) {
 decomp = createDecompressor(codecName);
 decompressors.put(codecName, decomp);
 }
 return decomp;
}

</code>

 

If multiple threads try to read the pages belonging to different columns, they run into thread

safety issues. This issue prevents increasing the throughput at which applications can read parquet data by parallelizing page reads. 



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