This document is a collection of best practices for Wrangler CSV parsing and cleansing of CSV files.
General Tips
Avoid using automatic header detection with parse-as-csv directive(parse-as-csv :col â\tâ false). On large files that are distributed across multiple partitions, header line which is the first line of CSV is not present. This will either result in failure or records will be lost.
If you have to use parse-as-csv directive, then make sure, the files are smaller than 128MB (lowest data block).