adriangb commented on PR #9628:
URL: https://github.com/apache/arrow-rs/pull/9628#issuecomment-4162471419

   > > > Yea, I think we can deprecate the old behavior and maybe remove it 
after few releases.
   > > 
   > > 
   > > Do you want to do that in this PR or in a followup (maybe once this is 
out in the wild and known to be working well)?
   > 
   > I think we can do it in this PR.
   
   If we want to deprecate the existing NDV I think we're better off 
re-interpreting it to mean "maximum ndv" or "initial ndv". That way existing 
users who are setting the ndv also benefit from folding. This means there will 
be no way to disable folding but I also don't see any reason anyone would want 
to do that beyond requiring a fixed-size bloom filter (in which case relying on 
a combination of fpp + ndv giving you a fixed size was probably a bad choice to 
begin with given I don't think we made any such API promise, and they should 
open an issue requesting an explicit API for this).
   
   Thus the only changes vs. main now are:
   1. Adding the folding on write.
   2. Default max ndv is derived from the max rows per row group instead of 
being hardcoded.


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