1) If you use a field that will be in the final table in your AutoGenerate 0, then you will not need a drop field statement. Make sure you use '' for text and 0 for numerics as Qlik uses the first time it sees the field to infer the data type.
2) You can stage the xlsx files as qvds in a 2 tier ETL if you like, and this will improve performance if the staging load only happens once per day and the main document reloads may happen several times a day, or you are loading a bunch of invariant history files on every load.
Logic will get you from a to b. Imagination will take you everywhere. - A Einstein
Observed that the high load time was due to the Load * from second part of the excel. Due to the bad file format, instead of 20-25 columns , 16,000+ columns are getting loaded from each file. which means 16000 * no. of files would get loaded each time.
i tried to get only required columns loaded, did not work. Could you please let me know if there is a way to restrict the number of columns to be loaded while doing a load*.