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From Cheng Lian <lian.cs....@gmail.com>
Subject Re: [ compress in-memory column storage used in sparksql cache table ]
Date Wed, 02 Sep 2015 08:44:08 GMT
Yeah, two of the reasons why the built-in in-memory columnar storage 
doesn't achieve comparable compression ratio as Parquet are:

1. The in-memory columnar representation doesn't handle nested types. So 
array/map/struct values are not compressed.
2. Parquet may use more than one kind of compression methods to compress 
a single column. For example, dictionary  + RLE.

Cheng

On 9/2/15 3:58 PM, Nitin Goyal wrote:
> I think spark sql's in-memory columnar cache already does compression. Check
> out classes in following path :-
>
> https://github.com/apache/spark/tree/master/sql/core/src/main/scala/org/apache/spark/sql/columnar/compression
>
> Although compression ratio is not as good as Parquet.
>
> Thanks
> -Nitin
>
>
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