Aims

• start becoming familiar with the PostgreSQL source code
• practice the edit-make-install-test cycle for modifying PostgreSQL

Exercise

The psql client in earlier versions of PostgreSQL used to have a much friendlier introductory message than the current version. Nowadays, all that greets you when you start an interactive psql session is:

$ psql mydb
psql (9.4.6)
Type "help" for help.

mydb=#

Your task for this lab is simply to make the introductory message more friendly. You must change the code for psql so that it now behaves as follows:

$ psql mydb
Welcome to the PostgreSQL 9.4.6 version of psql
Type "help" for help.

mydb=#

You should display this behaviour only when the user successfully connects to a database. All other invocations of psql should appear the same as before.

Simple, eh? It would be if you were familiar with the PostgreSQL code-base. However, you'll need to work a few things out to accomplish this:

• where is the source code for psql?
• where is the code that prints the introductory message?
• how do I re-install the psql client once I've changed it?
• what kind of testing should I do to make sure I haven't broken something else?

Here are a few small hints to get you started. Since this is an exploratory lab, the idea is for you to work it our for yourself.

• the source code for clients lives under postgresql-9.4.6/src/bin
• change into the directory where the psql source code is located
• find the source code file containing the main function (use grep)
• look for the string containing the help message
• you only need to change a single line of code
• run make and make install from within that directory
• since you're recompiling a client, there's no need to stop the server when you re-make psql

Some things not to do:

• don't run make from the top-level postgresql-9.4.6 directory
  (it's too slow and reinstalls a whole bunch of stuff that hasn't actually changed; sloppy Makefile, I'd say)
• don't spend more than an hour on this exercise ... unless you start to find the source code exciting

End of Prac

Let me know via the MessageBoard or come to a consultation if you have any problems with this exercise ... jas