[ TOC ] [ Previous ] [ Next ]

# 3. GETTING STARTED WITH POSTGRES

This section discusses how to start POSTGRES and set up your own environment so that you can use frontend applications. We assume POSTGRES has already been successfully installed. (Refer to the installation notes for how to install POSTGRES.)

Some of the steps listed in this section will apply to all POSTGRES users, and some will apply primarily to the site database administrator. This site administrator is the person who installed the software, created the database directories and started the postmaster process. This person does not have to be the UNIX superuser, "root," or the computer system administrator. In this section, items for end users are labelled "User" and items intended for the site administrator are labelled "Admin." Throughout this manual, any examples that begin with the character ``%'' are commands that should be typed at the UNIX shell prompt. Examples that begin with the character ``*'' are commands in the POSTGRES query language, POSTGRES SQL.

## 3.1. Admin/User: Setting Up Your Environment

Figure 2. shows how the POSTGRES distribution is laid out when installed in the default way. For simplicity, we will assume that POSTGRES has been installed in the directory /usr/local/postgres95. Therefore, wherever you see the directory /usr/local/postgres95 you should substitute the name of the directory where POSTGRES is actually installed. All POSTGRES commands are installed in the directory /usr/local/postgres95/bin. Therefore, you should add this directory to your shell command path. If you use a variant of the Berkeley C shell, such as csh or tcsh, you would add

             % set path = ( /usr/local/postgres95/bin $path )

in the .login file in your home directory. If you use a variant of the Bourne shell, such as sh, ksh, or bash, then you would add

             % PATH=/usr/local/postgres95/bin:$PATH
             % export PATH

to the .profile file in your home directory. From now on, we will assume that you have added the POSTGRES bin directory to your path. In addition, we will make frequent reference to "setting a shell variable" or "setting an environment variable" throughout this document. If you did not fully understand the last paragraph on modifying your search path, you should consult the UNIX manual pages that describe your shell before going any further.

## 3.2. Admin: Starting the Postmaster

It should be clear from the preceding discussion that nothing can happen to a database unless the postmaster process is running. As the site administrator, there are a number of things you should remember before starting the postmaster. These are discussed in the section of this manual titled, "Administering POSTGRES." However, if POSTGRES has been installed by following the installation instructions exactly as written, the following simple command is all you should need to start the postmaster:

             % postmaster &

The postmaster occasionally prints out messages which are often helpful during troubleshooting. If you wish to view debugging messages from the postmaster, you can start it with the -d option and redirect the output to the log file:

             % postmaster -d >& pm.log &

If you do not wish to see these messages, you can type

             % postmaster -S

and the postmaster will be "S"ilent. Notice that there is no ampersand ("&") at the end of the last example.

## 3.3. Admin: Adding and Deleting Users

The createuser command enables specific users to access POSTGRES. The destroyuser command removes users and prevents them from accessing POSTGRES. Note that these commands only affect users with respect to POSTGRES; they have no effect administration of users that the operating system manages.

## 3.4. User: Starting Applications

Assuming that your site administrator has properly started the postmaster process and authorized you to use the database, you (as a user) may begin to start up applications. As previously mentioned, you should add /usr/local/postgres95/bin to your shell search path. In most cases, this is all you should have to do in terms of preparation.1 If you get the following error message from a POSTGRES command (such as psql or createdb):

             connectDB() failed: Is the postmaster running at 'localhost' on port '4322'?

it is usually because (1) the postmaster is not running, or (2) you are attempting to connect to the wrong server host. If you get the following error message:

             FATAL 1:Feb 17 23:19:55:process userid (2360) !=
               database owner (268)

it means that the site administrator started the postmaster as the wrong user. Tell him to restart it as the POSTGRES superuser.

## 3.5. User: Managing a Database

Now that POSTGRES is up and running we can create some databases to experiment with. Here, we describe the basic commands for managing a database.

### 3.5.1. Creating a Database

Let's say you want to create a database named mydb. You can do this with the following command:

             % createdb mydb

POSTGRES allows you to create any number of databases at a given site and you automatically become the database administrator of the database you just created. Database names must have an alphabetic first character and are limited to 16 characters in length. Not every user has authorization to become a database administrator. If POSTGRES refuses to create databases for you, then the site administrator needs to grant you permission to create databases. Consult your site administrator if this occurs.

### 3.5.2. Accessing a Database

Once you have constructed a database, you can access it by:

- running the POSTGRES terminal monitor programs ( monitor or psql) which allows you to interactively enter, edit, and execute SQL commands.
- writing a C program using the LIBPQ subroutine library. This allows you to submit SQL commands from C and get answers and status messages back to your program. This interface is discussed further in section ??.

You might want to start up psql, to try out the examples in this manual. It can be activated for the mydb database by typing the command:

             % psql mydb

You will be greeted with the following message:

             Welcome to the POSTGRES95 interactive sql monitor:

                type \? for help on slash commands
                type \q to quit
                type \g or terminate with semicolon to execute query
              You are currently connected to the database: mydb

             mydb=>

This prompt indicates that the terminal monitor is listening to you and that you can type SQL queries into a workspace maintained by the terminal monitor. The psql program responds to escape codes that begin with the backslash character, "\". For example, you can get help on the syntax of various POSTGRES SQL commands by typing:

             mydb=> \h

Once you have finished entering your queries into the workspace, you can pass the contents of the workspace to the POSTGRES server by typing:

             mydb=> \g

This tells the server to process the query. If you terminate your query with a semicolon, the \g is not necessary. psql will automatically process semicolon terminated queries. To read queries from a file, say myFile, instead of entering them interactively, type:

             mydb=> \i fileName

To get out of psql and return to UNIX, type

             mydb=> \q

and psql will quit and return you to your command shell. (For more escape codes, type \h at the monitor prompt.) White space (i.e., spaces, tabs and newlines) may be used freely in SQL queries. Comments are denoted by --. Everything after the dashes up to the end of the line is ignored.

### 3.5.3. Destroying a Database

If you are the database administrator for the database mydb, you can destroy it using the following UNIX command:

             % destroydb mydb

This action physically removes all of the UNIX files associated with the database and cannot be undone, so this should only be done with a great deal of fore-thought.

1. If your site administrator has not set things up in the default way, you may have some more work to do. For example, if the database server machine is a remote machine, you will need to set the PGHOST environment variable to the name of the database server machine. The environment variable PGPORT may also have to be set. The bottom line is this: if you try to start an application program and it complains that it cannot connect to the postmaster, you should immediately consult your site administrator to make sure that your environment is properly set up.

[ TOC ] [ Previous ] [ Next ]