PostgreSQL: Installation and configuration

Here's another plug for FreshPorts.  I've been playing with ideas and I've come up a few good improvements.  But they will require a database with more features than mySQL.  Specifically, I'm going to need stored procedures and functions.I actually installed PostgreSQL back in late July, but never did anything with it.  This article will help you along the way. PostgreSQL caught my attention because it's been recommended by others.  It also has the stored procedures and triggers.   These facilities will form the heart and soul of the new database. NOTE: Since this article was written, the path for the PostgreSQL binaries has changed. When I wrote this article, the pathnames were /usr/local/pgsql/bin/. I have since updated the article to refer to the new location /usr/local/bin/.

Installation - from ports

If you want to use php first, well, I've already installed that.  I'm not sure what you'd do if you want PostgreSQL and php.  Perhaps install mod_php later.  Does anyone know?  If so, add your comments.As always, I'm installing this from ports.  If you haven't already installed your ports tree, you should.  Because this is how easy it is to install a port: # cd /usr/ports/databases/postgresql7/ # make install There.  Done. Actually, I'm sure there might have been more to it than that.  Such as specifying php options.  But I can't recall. You also need to initialize the database with the following command [note that the user pgsql is not used on all systems, on some systems it might be postgres): # su -l pgsql -c initdb This database system will be initialized with username "pgsql". This user will own all the data files and must also own the server process. Creating directory /usr/local/pgsql/data Creating directory /usr/local/pgsql/data/base Creating directory /usr/local/pgsql/data/global Creating directory /usr/local/pgsql/data/pg_xlog Creating template1 database in /usr/local/pgsql/data/base/1 [snip] Success. You can now start the database server using:     /usr/local/bin/postmaster -D /usr/local/pgsql/data or     /usr/local/bin/pg_ctl -D /usr/local/pgsql/data -l logfile start NOTE: Recent versions of FreeBSD will require this entry in /etc/rc.conf in order for PostgreSQL to start: postgresql_enable="YES" Now I'm ready to start the database server: /usr/local/etc/rc.d/010.pgsql.sh start NOTE: in recent versions of PostgreSQL (e.g. 8.2), the command is: /usr/local/etc/rc.d/postgresql start That should be the name of the file (i.e. 010.pgsql.sh) but if you can't find it, just hunt around in that directory for a simlarly named file.

Allowing users to use psql

This section documents the steps required to allow a user to access a database.  You may also want to read the instructions for adding a database user.  In this section, the term user refers to a login.I like the way PostgreSQL works.  It creates a special user for you, pgsql.  This user does all the work.  The database runs as this user, and all work (database creation, adding users, etc) is done as this user. NOTE: pgsql is not used on all systems, on some systems it might be postgres. The first step is to add myself as a user, so I don't have to do all my work as pgql.  Here's how I added myself as a user.  I typed the bits in bold. See also the NOTE below regarding the path. $ su -l Password: [root@set:~] # su pgsql $ /usr/local/bin/createuser dan Shall the new user be allowed to create databases? (y/n) y Shall the new user be allowed to create more new users? (y/n) y CREATE USER Done.  Now that I've added myself as a user who can create databases, I can use my normal login. NOTE: In more recent versions of PostgreSQL, the binary is /usr/local/bin/createuser.

Adding a database

Now I dropped back to my usual login and created a database. $ logout [root@set:~] # logout [dan@set:/usr/home/dan] $ /usr/local/bin/createdb mydb CREATE DATABASE Done.

Creating a user for this database

Now I dropped back to my usual login and created a database. $ /usr/local/bin/psql mydb Welcome to psql, the PostgreSQL interactive terminal. Type: \copyright for distribution terms \h for help with SQL commands \? for help on internal slash commands \g or terminate with semicolon to execute query \q to quit mydb=# Now I'll create a user, tester,  for this database. mydb=# create user tester with password 'mypassword'; CREATE USER To remove a user: mydb=# drop user tester; DROP USER NOTE: In recent versions of PostgreSQL, CREATE USER has been deprecated by CREATE ROLE.

Creating groups

You can also create groups and place the users in those groups.  You can grant permissions collectively to the group instead of individually to the user. mydb=# CREATE GROUP testers WITH USER dan; CREATE GROUP Then you can grant SELECT permission on table thedata   permissions to group testers: mydb=# GRANT SELECT ON thedata TO GROUP testers; CHANGE

Creating a table

I created a rather simple table for my testing. mydb=# create table test (id serial, name varchar(10)); NOTICE: CREATE TABLE will create implicit sequence 'test_id_seq' for SERIAL column 'test.id' NOTICE: CREATE TABLE/UNIQUE will create implicit index 'test_id_key' for table 'test' CREATE Then I inserted data: mydb=# insert into test (name) values ('test'); INSERT 18879 1 mydb=# insert into test (name) values ('test2'); INSERT 18880 1 Then I read that data back out: freshports2=# select * from test; id | name ----+------- 1 | test 2 | test2 (2 rows)

Getting php going

I create a simple php test in an existing website.  For help on creating websites, look at Apache - virtual hosts.I added this to testpsql.php3 in my website.  Note the amended while loop at the end of this section. <head> <title>PostgreSQL test</title> <body> <?php $database=pg_connect("dbname=mydb user=test password=mypassword"); if ($database) { $result = pg_exec ($database, "select * from test"); if ($result) { echo pg_numrows($result) . " rows to fetch\n"; echo "<table>\n"; $i = 0; while ($myrow = pg_fetch_array ($result, $i)) { $i++; echo " <tr><td>" . $myrow["id"] . "</td><td>" . $myrow["name"] . "</td></tr>\n"; if ($i > 10) break; } echo "</table>\n"; } else { echo "read from test failed"; } pg_exec ($database, "end"); } else { echo "no connection"; } ?> </body></html> As you can see, I had to manually break the loop.  I have no idea why.  I thought pg_fetch_array would return false at the end of the result set, as mentioned in the documentation.  But it didn't.  So far, it appears I'll have to use a for  loop for that and not a while.  Any ideas on why should be added as comments.  pg_fetch_array was behaving like that?  It seems to be standard behaviour. A search at http://google.com found this example, which I used to create this amended while loop: for ($i = 0; $i < $NumRows; $i++) { $myrow = pg_fetch_array ($result, $i); echo " <tr><td>" . $myrow["id"] . "</td><td>" . $myrow["name"] . "</td></tr>\n"; }

What's next?

I would like a Windows GUI inteface to PostgreSQL.  Any suggestions should be added to the comments.   I found ZEOS, but couldn't get it to connect.  I suspect someone wrong with my access rights, but I was looking at /usr/local/pgsql/lib/pg_hba.conf.I'm sure the next PostgreSQL article will have more information.

backups

It's time I added backups to this article.  This information is taken from the Admin documentation at /usr/local/share/doc/pgsql/admin/.A backup is done with this: % pg_dump dbname > dbname.pgdump A restore is done with this: cat dbname.pgdump | psql dbname Depending upon your path settings, you may have to specify the full path to these binaries.  Under FreeBSD, this would be /usr/local/bin/pg_dump. For a backup script, please read the section on mySQL backups in the article I wrote for mySQL. Just substitute pg_dump for mysqldump.

Various notes

Tonight I was upgrading, accidentally mind you, from 7.0.3 to 7.1.3. I did this without first deinstalling the old version. Bad idea. As a precaution, you should always dump your old databases before upgrading. I didn't. When I tried to run psql, I was getting these errors: # psql FreshPort2Test psql: FATAL 1: SetUserId: user 'root' is not in 'pg_shadow' The mistake was that I was doing this as root. DOH! I had created all my databases as dan. So asking on IRC, I was told to do this: # su - pgsql # psql FreshPort2Test That worked. I then dumped all my databases as shown in a previous section. Then I saved them all to CD. Then I did the right thing: # pkg_delete -f postgresql-7.0.3 # pkg_delete -f postgresql-7.1.3 # cd /usr/ports/databases/postgresql7 # make deinstall # make install Then I had to do the initdb manually (and I'm not sure if this is usually done automatically): # su -l pgsql $ initdb This database system will be initialized with username "pgsql". This user will own all the data files and must also own the server process. Creating directory /usr/local/pgsql/data Creating directory /usr/local/pgsql/data/base Creating directory /usr/local/pgsql/data/global Creating directory /usr/local/pgsql/data/pg_xlog Creating template1 database in /usr/local/pgsql/data/base/1 DEBUG: database system was shut down at 2001-11-29 17:59:29 EST DEBUG: CheckPoint record at (0, 8) DEBUG: Redo record at (0, 8); Undo record at (0, 8); Shutdown TRUE DEBUG: NextTransactionId: 514; NextOid: 16384 DEBUG: database system is in production state Creating global relations in /usr/local/pgsql/data/global DEBUG: database system was shut down at 2001-11-29 17:59:34 EST DEBUG: CheckPoint record at (0, 108) DEBUG: Redo record at (0, 108); Undo record at (0, 0); Shutdown TRUE DEBUG: NextTransactionId: 514; NextOid: 17199 DEBUG: database system is in production state Initializing pg_shadow. Enabling unlimited row width for system tables. Creating system views. Loading pg_description. Setting lastsysoid. Vacuuming database. Copying template1 to template0. Success. You can now start the database server using: /usr/local/bin/postmaster -D /usr/local/pgsql/data or /usr/local/bin/pg_ctl -D /usr/local/pgsql/data -l logfile start $ Then I started the database server: # /usr/local/etc/rc.d/010.pgsql.sh start NOTE: in recent versions of PostgreSQL (e.g. 8.2), the command is: # /usr/local/etc/rc.d/postgresql start Note that this script had been sitting around from my previous install. It may not be the same name on your system, but it will be in the same directory.

Improving performance

If you find that a query isn't running fast enough, look at the situation and act accordingly. Here is an example I encountered when working on FreshSource. I was looking for all the children of a particular element: freshports=# select * from element where parent_id = 77340; id | name | parent_id | directory_file_flag | status -------+----------+-----------+---------------------+-------- 77341 | files | 77340 | D | A 77449 | Makefile | 77340 | F | A 77450 | distinfo | 77340 | F | A (3 rows) freshports=# explain analyse select * from element where parent_id = 77340; NOTICE: QUERY PLAN: Seq Scan on element (cost=0.00..2165.41 rows=11 width=30) (actual time=548.68..655.47 rows=3 loops=1) Total runtime: 655.59 msec As you can see, this query is accomplished by doing a sequential scan on the element table and it takes 0.6s. Let's refresh the statistics on this table, and then run the query again. freshports=# vacuum analyze element; VACUUM freshports=# explain analyse select * from element where parent_id = 77340; NOTICE: QUERY PLAN: Seq Scan on element (cost=0.00..2201.85 rows=12 width=30) (actual time=178.50..236.41 rows=3 loops=1) Total runtime: 236.53 msec That gets us down to 0.2s, but we are still doing a sequential scan. Let's try an index. freshports=# create index element_parent_id on element(parent_id); CREATE freshports=# explain analyse select * from element where parent_id = 77340; NOTICE: QUERY PLAN: Index Scan using element_parent_id on element (cost=0.00..25.89 rows=12 width=30) (actual time=0.38..0.49 rows=3 loops=1) Total runtime: 0.62 msec OK, now that is impressive. We've gone from 600ms to 0.6ms. That's 1000 times faster overall. For more information, read the documentation regarding vacuum.