file_put_contents将行附加到PHP中的CSV文件

If I have a CSV file with 5000 rows on my server, does file_put_contents read the whole file into memory before appending a new row?

I have a custom tracker PHP script that appends one line to a server side CSV file each time a new web visitor comes.

With 100 or so visitors, the CSV file is small, and the script is fast.

But with high numbers - I am wondering if my PHP script will slow down when appending a new row?

Thanks