Bigdata SQL: File Formats Text/CSV Files

Comma-separated values (CSV) files do not support block compression, thus compressing a CSV file in Hadoop often comes at a significant read-performance cost.
When working with Text/CSV files in Hadoop, never include header or  footer lines. Each line of the file should contain a record. This means that there is no metadata stored with the CSV file. One must know how the file was written in order to make use of it. File structure is dependent on field order: new fields can only be appended at the end of records, while existing fields can never be deleted. As such, CSV files have limited support for schema evolution.