modifying the source code

HI,

I am asking this question is because I need to modify the open source software of postgres and I completely have no idea on how to start the project.

Here is more details. I usually work on Linux and use GNU compiler. So far, the project that I wrote is less than 10 files (with vim, no IDE so far). I usually compile them separately and put them together as a single executable file.

Now I need to modify the postgres source code. The source of it contains hundreds of files which is too much for me.

I need to understand it, make a small modification and add some functions or subroutines in the software as new features.

Could you tell me where to start? 

I am using the eclipse IDE to modify the source code of postgres. I was trying to modify a particular function, so I commented some of the lines , and made the function return a constant, after that I tried to debug the source code. But now it is returning an error.

PS :- I do know that the documentation of the source code exists here

http://www.postgresql.org/developer/coding/ . I went through it, but could not completely understand it.can someone explain me in lay man terms.

Thanks.

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