It looks like there's a race condition between two goroutines: one that reads input data and one that bulk inserts data. The "count insertions" code is on the bulk insert side as is optimistic – increment a counter for document queued to send and then decrement later for errors after the bulk is flushed to the database. Because the error reading data aborts the program early, it can report the number of insertions (queued) rather than the number actually sent to the server.