[BEGINNER] Trying to write efficient code

I am writing small, simple script that deals with a flat-file database. It only uses 1 text file for this and it is quite small at the moment. However, this text file has the potential to become big because as my script is used, it continually adds new information to this text file.

To keep it simple, this is what my script does: It adds a new line to the top of the db file.

I have two options here:

1. Load the entire db file into a list (memory),
unshift new line,
then write it back into the file.

2. Create a temporary file,
write new line to temp file,
using a while loop (line-by-line) write the entire db file into the temp file,
then replace (rename) the original db file with the newer temp file.

It seems to me that option 2 is better because it doesn't load the entire file into memory. Of course, I'm just a novice and drawbacks are not as obvious to me.

So I guess my questions are: Am I correct in my assumption that option 2 is better? Or am I missing something? Is one option more cpu-intensive than the other?

>>2
But then when I try to read the db file, I would need to reverse the order so that the most recent entry is at the top. If I remember correctly, that would involve having to write the entire file into memory anyways so I might as well use option 1.