Question about debugger

Hello,

I'm a student who use postgresql. I'd like to debug postgres source code.I
tried to use "ddd" in linux. The thing what I want to do is debugging
backend part.How can I do that. The commands that I used until now are
following.

1. ddd postgres
2. In the ddd,I tried to attach pid. (but I can't find pid about backend)
3. When I tried to run program with break point,I met error like "can't
find 2003-10-15(that is the date and time when I run)".

So,I'm not sure how can I use "ddd". Could let me know how can I use this?