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https://issues.apache.org/jira/browse/PARQUET-1641?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16917118#comment-16917118
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ASF GitHub Bot commented on PARQUET-1641:
-----------------------------------------
samarthjain commented on pull request #668: PARQUET-1641 Parquet pages for
different columns cannot be read in parallel
URL: https://github.com/apache/parquet-mr/pull/668
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> 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
> Priority: Major
> Labels: pull-request-available
>
> 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:java}
> 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:java}
> @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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