That however only impacts CSVs or other text files, where the compression is the envelope. In parquet, it is the internal chunks that are compressed, so it is as parallelizable as ever.

Also, generic CSV is not parallelizable anyway, because it allows you to have (quoted) newlines inside fields and then there is really now way to split it on newlines because you never know if you're on beginning or row or in the middle.

So parallel reading of CSVs is more of a optimization for specific CSVs that you know don't have newlines inside fields.