You infer the types of the source data. For example you can go through say 1% of your data and for each column see if you can coerce all of the values to a flo

You infer the types of the source data. For example you can go through say 1% of your data and for each column see if you can coerce all of the values to a float, int, date, string etc. And then from there you can set the Parquet schema with proper types.