alamb commented on PR #23492:
URL: https://github.com/apache/datafusion/pull/23492#issuecomment-5273121874

   I have been thinking about this PR and how it could play into our "turn 
pushdown on by default" story
   
   We have put a lot of work in upstream to make applying filters during 
parquet decoding faster  (thanks to @hhhizzz @haohuaijin and many others). 
However, enabling filter pushdown today **also** changes the I/O patterns (so 
that the all the needed columns are not fetched up front, but instead are 
fetched sequentially)
   
   I think one thing we could do with a nice I/O pre-fetching abstraction would 
be to start a request to fetch bytes for all columns required in a single 
request, so the I/O pattern is the same -- and then just enable the pushdown 
filter application once we already had the data 🤔 


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