Schedule 13D is a form that must be filed with the U.S. Securities and Exchange Commission (SEC) when a person or group acquires more than 5% of a voting class of a company's equity shares.

The problem I've noticed is that if I append the file with each of the 100k runs (one at a time), it can happen that two threads try to save to the file at the same time and some row (s) end up empty.