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https://issues.apache.org/jira/browse/HIVE-7859?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14129021#comment-14129021
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Gopal V commented on HIVE-7859:
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I did try BEST_COMPRESSION, but without much improvement.
Time taken: 1720 seconds - 152.5Gb
My conclusion about that is that ORC already does a large amount of the RLE,
dictionary and bit-packing optimizations.
We are not getting anything significant by burning ~3x CPU in Zlib which do the
same steps again, to no avail.
> Tune zlib compression in ORC to account for the encoding strategy
> -----------------------------------------------------------------
>
> Key: HIVE-7859
> URL: https://issues.apache.org/jira/browse/HIVE-7859
> Project: Hive
> Issue Type: Bug
> Components: File Formats
> Reporter: Gopal V
> Assignee: Gopal V
> Attachments: HIVE-7859.1.patch, HIVE-7859.2.patch
>
>
> Currently ORC Zlib is slow because several compression strategies ZLib uses
> is already done by ORC in itself (dictionary, RLE, bit-packing).
> We need to pick between Z_FILTERED, Z_HUFFMAN_ONLY, Z_RLE, Z_FIXED and
> Z_DEFAULT_STRATEGY according to column stream type.
> For instance an RLE_V2 stream could a use Z_FILTERED compression without
> invoking the rest of the strategies.
> The string streams can use Z_FIXED compression strategies and so on.
> The core limitation to stick to retain compatibility with the default
> decompressor, so that these are automatically backward compatible.
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