PokerTracker

PostgreSQL

What do I need it for? Why there is a PT3 available WITHOUT it?

Simple questions, simple answers, please.

PostgreSQL is a database server. In particular it is the database that PokerTracker 3 uses to store all of its data. PokerTracker 3 cannot run without PostgreSQL because otherwise it would have no place to store its data or read the data from.

The "with" and "without" versions available for download are with or without the PostgreSQL installer, so that people who already have PostgreSQL installed do not have to redownload and reinstall it, but that people who are new with us can get one package instead of two (with some options streamlined, as well).

Thank you for all your information.

Do I have to use username "postgre" and default passwords, to access Pt3?

The username needs to be 'postgres', yes.
You should be able to change the password if you want to, but make sure you keep a note of it. However, if you install PT3 with Postgres, all of this should be handled for you.

Why do I need the passwords? And why the username must be 'postgres'?

There is a default level of security in the database program. The default password is 'dbpass'. The default username is postgres simply because that's what the people who wrote the program thought it should be. You can disable the password authentication, though, by following the steps of this tutorial.