Re: [I] [C++][Parquet] Use PLAIN as default encoding for float32 and float64 columns in Parquet writer [arrow]

["pitrou (via GitHub)" <gi...@apache.org>]

pitrou commented on issue #49715:
URL: https://github.com/apache/arrow/issues/49715#issuecomment-4682682282

   I remember @xhochy (or was it someone else?) pointing out that in many workloads, floating-point values are actually well-compressible using dictionary encoding.
   
   Ideally this would be adaptative, but that might require a significant architectural refactoring.
   
   One thing is that we have a max dictionary page size setting, but we could also have a max relative dictionary cardinality setting. The idea being that if the dictionary cardinality is greater than a given fraction (e.g. 10%) of the total number of encoded values, we would switch to PLAIN or BYTE_STREAM_SPLIT.
   


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