PostgreSQL for Data Architects | Data | Paperback (original) (raw)

Installation options

There are many possible ways to install PostgreSQL on a system. For Windows, downloading the Graphical Installer and using this is the easy way. For Linux systems such as Red Hat Enterprise Linux or CentOS, we could either use Yellow dog Updater Modified (yum) or Red Hat Package Manager or RPM Package Manager (rpm) commands to install PostgreSQL. For Ubuntu, PostgreSQL can be installed using the apt-get command, which in turn works with Ubuntu's Advanced Packaging Tool (APT). While these options work, we do not get to see what is happening when we execute these commands, except, of course, that the database gets installed.

Then there are situations where we might want to build from the source. Assume that all we have is one production server and one development or staging server. We are on version 9.3. Version 9.4 is about to be released and there are quite a few interesting features in 9.4 that we want to try out. If we want to install 9.4 in the test server and use it alongside 9.3, without the installations stepping on each other's toes, compiling from the source with the --prefix= option and specifying different installation directories is the right approach. We could also set different default ports. It's also possible that the new version (source) is ready, but the package for our Linux distribution is not ready yet.

We might use a flavor of Linux for which an installation package is not available at all. Installation from source is the way forward in these situations. One advantage with installing from the source is that we don't have to worry too much about which package to download, the version of operating system (CentOS 6.3 or 6.4?), architecture (32 bit or 64 bit), and so on. These are more or less irrelevant. Of course, we should be using an operating system/architecture that is supported by the database, but that's about it! We also need to download and install all the tools and utilities necessary to compile and make the software, in this case, PostgreSQL.

So let's get down to it.

Downloading and extracting the source

The source for PostgreSQL is available at http://www.postgresql.org/ftp/source/.

We can see a number of versions all the way down to version 1 when it was called Postgres95 and up to the latest production and beta versions. If you belong to the group who believe that one shouldn't try software that is not at least a few months old, so that its teething issues are resolved, you should opt for the last-but-one version. It's a good idea to opt for the latest stable version. The latest versions have added quite a few very useful features, such as materialized views and an improved set of JSON functions and operators.

We will use the following wget command to download the source:

wget http://ftp.postgresql.org/pub/source/v9.3.0/postgresql-9.3.0.tar.gz

Note

It's a good idea to opt for the latest stable version.

Executing this command will give us a window that looks like this:

Downloading and extracting the source

As we can see, the tarred and gzipped source code comes to about 21 MB. As an aside, the installation files of Oracle—the big RDBMS out here—weighs over 2.2 GB.

The files can be extracted using the following command:

tar -xvf postgresql-9.3.0.tar.gz

The tar command is used to create or extract TapeARchive files. In the preceding command, the x option is used to extract, v for verbose is used so that we can see the list of files and folders getting extracted, and the f option is for, well, passing the name of the file, which will undergo the extraction process. We might need to provide the z option, so the command will be tar -xzvf if the preceding code in the tar command does not work. Some versions of tar are intelligent enough to figure out whether it is a gzipped file or not and will unzip it automatically. The untarred unzipped files come to around 115 MB.

Inspecting the contents

Let's inspect the contents:

cd postgresql-9.3.0

find ./ -maxdepth 1 -type d

The find command searches for files meeting specific criteria. Here, we instructed find to limit itself to scanning just one level of subdirectories using maxdepth 1. We used the type option along with d to tell find that we need files of type directory, as shown in the following screenshot:

Inspecting the contents

There are four directories:

Now let's move on to the dependencies, configuration options, and the actual installation itself.

Dependencies to compile the source

To compile and build PostgreSQL from source, we need GNU Make Version 3.8 or higher. The gmake -v command will tell us whether we have gmake and its version.

A compiler is also necessary. GNU Compiler Collection (GCC) is one such toolset that is included in almost all the Unix systems. The gcc -v command will provide you with the version of gcc as well as options with which it was configured on the system, as shown in the following screenshot:

Dependencies to compile the source

Note

We can use the following commands to install the necessary packages if they are missing:

The process of building a package from source involves preprocessing the source (including the header files, expanding macros, and so on), compiling, assembly, and linking (linking the libraries). The make utility automates the process of building the executable from source code. The make command uses a makefile, which contains rules on how to build the executables.

Other than GNU Make and a compiler, there is nothing else that is really necessary to continue. However, it is better to have at least the following two components:

Adding SQL/XML support will also be useful as sooner or later we will want to extract data from tables in an XML format or load data from the XML files to tables. Still, this might not be as useful as the other two, namely, readline and zlib.

Configuring and creating the makefile

The next step is to execute configure. This is a shell script which will run, to quote documentation, a number of tests to determine several system dependent variables. It will also create many files that will be used during compilation. We can get an idea about the options by executing the following command:

./configure --help > /tmp/config.txt

We can vi /tmp/config.txt and verify that there are over 80 options that can be used. These options can be broadly grouped into the following categories:

Tip

Pay attention to the --prefix option. If you would like to do a clean upgrade without causing disruption to the existing environment, provide a directory in which the installation files should be written to. This way, each version will be in a different directory. For example:
./configure --prefix=/opt/pg/9.3

When we run ./configure, it's likely that we get an output like this:

Configuring and creating the makefile

The output tells us that readline is not available. However, if we list installation packages, it is very much there. The reason is that readline-devel is missing. It contains files needed by programs (such as psql) that use the readline library. This can be installed using the following command:

yum install readline-devel.x86_64

It also installs ncurses-devel. You will have to execute the command using sudo or root. You might also get a similar error for zlib, although zlib itself is already installed. Again, the corrective action is to install devel, in this case, zlib-devel.

Once this is done, we can run configure again and it should go through without any issues, as shown in the following screenshot:

Configuring and creating the makefile

The two files are now created in the current directory in addition to a few more files in subdirectories. One is config.status and the other (config.log. config.status) is a bash script that can be executed to recreate the configuration. The config.log file can be reviewed to understand the various options used, variables, and errors, if any. It's possible that the config.log file has a few errors that are marked fatal, and the compilation process can still be completed without any issue.

Building and creating the executables

This step compiles all the source files and generates the executables. The makefile created in the configure step is used by the gmake utility. These files are not copied to standard directories, such as bin, /usr/bin, /usr/local/bin, and so on. We have the option to make all the options available (the contrib modules, source, and so on), or just the core. It's also possible to build just the core now and add the necessary contrib modules later on. We will build everything now, rather than adding the necessary modules later. Hence, the command is:

The process takes a few minutes to complete, and in the end says PostgreSQL, contrib, and documentation successfully made. Ready to install, as shown in the following screenshot:

Building and creating the executables

Installing and moving the files to where they belong

This is the step where the files are copied to the correct directories. As the installation process involves writing files to directories, which an ordinary user cannot write to, we need to use su for this step:

If you are interested in seeing what happens during the installation step, redirect the output to a file, for example, gmake install-world > /tmp/install.out.

We used the keyword world for make. We will use a similar option for installation too:

If all goes well, we will see a message that says PostgreSQL, contrib, and documentation successfully made. Ready to install. If the output was directed to a file as mentioned, we can open it and see that the installation process created a /usr/local/pgsql directory with a few subdirectories for various components. Then, the install command copied the directories and files to target directories and set attributes such as permissions. Refer to the highlighted portion in the following screenshot:

Installing and moving the files to where they belong

Inspecting the changes

As we did not make any changes to the default options, the installation files will be at /usr/local/pgsql. In this, we have four directories, namely include, lib, share, and bin. The include directory contains header files (.h) extension, and the lib directory contains all the libraries to be linked dynamically (.so in the case of Linux/Unix systems and .dll in the case of Windows systems). The bin directory, of course, contains executables.

It is the share directory that is a bit more interesting. Here, we have a number of sample files, namely, pg_hba.conf.sample, pg_ident.conf.sample, pg_service.conf.sample, postgresql.conf.sample, psqlrc.sample, and recovery.conf.sample. Once we initialize a cluster and make changes to various configuration files and then lose track of the changes, we can compare with these files and understand what changes have been made or roll back the changes if necessary.

This directory also has a few SQL files such as information_schema.sql and system_view.sql, which go into creating metadata views when a database cluster is initialized.

At the next level of directories under share, we have the doc directory that holds the documentation, and the man directory that holds the manual pages, and so on. The directory of interest under share is the one named extension. Here, we can see all the extensions, which we can install as per our need. Most extensions have a .control file that provides basic information, as shown here:

[jay@MyCentOS extension]$ more dblink.control # dblink extension comment = 'connect to other PostgreSQL databases from within a database' default_version = '1.1' module_pathname = '$libdir/dblink' relocatable = true

There will be SQL files that correspond to each extension, and these will be used when we install the extension in a database we choose.

The documentation to install PostgreSQL from source is at http://www.postgresql.org/docs/current/static/installation.html.

Note that we have just installed the database software. There is no database available to connect to yet. Adding a user for the database administration tasks and initializing a database cluster are the next steps.

Initializing a cluster

First we add an OS user. This user will be used to start/stop/restart the database. This user will also be the superuser for the cluster. The following command has to be executed as root or with sudo:

Tip

The new user need not be named postgres. It can be mydbadmin, mydba, or anything we fancy.

Next, we create a directory that will be the base directory for the new cluster. This could be anywhere. A standard location can be /usr/local/pgsql/data. However, you might want to have the database cluster on a separate partition. In the event of an OS and associated file system crash, your database data remains intact. It can also be that you want to use faster spinning disks or Solid State Disks for the database cluster to improve performance. In short, performance and/or reliability concerns can make you choose a location other than the default location to initialize the database cluster. As root, we execute the commands:

[root@MyCentOS extension]# mkdir -p /pgdata/9.3

The -p option ensures that the parent directory is also created if it is nonexistent:

[root@MyCentOS extension]# chown postgres /pgdata/9.3

Then, we switch user to postgres. This is necessary because when we initialize the cluster, the user under which the command was executed becomes the owner of the cluster. The server process will also be owned by this user. We will go with the standard user –postgres, which we created:

The next step is to run the initdb script. Well! Not exactly. If we run initdb now, we will get an error:

[postgres@MyCentOS ~]$ initdb -bash: initdb: command not found

This is because we haven't added the directory containing the PostgreSQL executables to the environment variable PATH yet. We could provide the absolute path and make it work. However, it is better to set the variables.

In .bash_profile of postgres, we have the following lines:

PATH=$PATH:$HOME/bin export PATH

Just before the export PATH line, add:

PATH=$PATH:/usr/local/pgsql/bin

Then, try this:

[postgres@MyCentOS ~]$ which initdb /usr/bin/which: no initdb in (/usr/local/bin:/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/sbin:/home/postgres/bin)

Not surprising, as .bash_profile doesn't get executed unless we source it or log out and log in. Log out, log in, and try again:

[postgres@MyCentOS ~]$ exit logout [root@MyCentOS ~]# su - postgres [postgres@MyCentOS ~]$ which initdb /usr/local/pgsql/bin/initdb

Now we are good to go! It's a good idea to execute the following:

Among the many parameters available, the important ones, in most cases, will be -D or --pgdata. This parameter is used to define the directory where the cluster will be initialized (where the database cluster should be stored). This is the only mandatory parameter. Another parameter that can be useful is --pwprompt. Using this, we can set the password for the database superuser. So, we execute the following command:

initdb --pgdata=/pgdata/9.3 --pwprompt

If this is not set now and password authentication is to be used, we have to set the password later, as shown here:

Initializing a cluster

As seen in the preceding screenshot, the process asks for the superuser password. Towards the end, it gives a warning that the trust authentication is enabled for local connections. This means that it will be possible to make connections from the localhost without being prompted for a password. It's a good idea to change this setting. We will come to this later. For more options available for initdb, please refer to http://www.postgresql.org/docs/current/static/app-initdb.html.

As always, let's see what happened; which directories got created when we initialized the cluster:

cd /pgdata/9.3 [postgres@MyCentOS 9.3]$ find ./ -maxdepth 1 -type d ./ ./base ./pg_stat ./pg_clog ./pg_xlog ./pg_tblspc ./pg_twophase ./pg_subtrans ./global ./pg_notify ./pg_stat_tmp ./pg_snapshots ./pg_multixact ./pg_serial

A quick walk through the directories

We will start the cluster as it will help us to relate the files system with the databases:

[postgres@MyCentOS base]$ expo rt PGDATA=/pgdata/9.3/

PGDATA is the default data directory location.

[postgres@MyCentOS base]$ pg_ctl start server starting [postgres@MyCentOS base]$ LOG: database system was shut down at 2013-10-13 13:48:07 IST LOG: database system is ready to accept connections LOG: autovacuum launcher started

The pg_ctl is a utility to start, stop, check the status, or restart the database cluster. Passing init or initdb as a parameter results in the initialization of a cluster. More options can be explored at http://www.postgresql.org/docs/current/static/app-pg-ctl.html.

Now, we will go through the directories:

In short, we have directories to hold containers of real user created data (tables and tablespaces), directories to hold data about all the data and data structures (metadata), and then directories to hold data about the state of transactions.

Processes created

Let's take a look at the processes spawned when we started PostgreSQL:

[root@MyCentOS ~]# ps -fupostgres

The following screenshot illustrates the processes spawned:

Processes created

We can see that there is one parent process (pid1566), which spawned a few child processes.

Important files created

One important file that gets created when we initialize a database cluster is postgresql.conf. This file contains a number of critical parameters related to the server processes and resource allocation, memory management, logging, file locations, and so on. Another file is pg_hba.conf."hba" (which stands for host-based authentication). Changes to these files are necessary to enable client connection to the database from a different machine. Both of these are in the PGDATA folder.

The postmaster.pid file in the same directory is used by pg_ctl to determine whether the database is running:

[postgres@MyCentOS 9.3]$ pg_ctl status pg_ctl: server is running (PID: 1566)

The contents of the file are as follows:

[postgres@MyCentOS 9.3]$ head -1 postmaster.pid 1566

The 1566 number in the pid file is the same as what we got for the parent process when we did a process listing earlier.

Working with extensions

We have so far initialized the database cluster. However, we made quite a few extensions available using the world option. What about them? We can list the installed extensions using the dx (describe extension) command at the psql prompt:

postgres=# \dx List of installed extensions Name | Version | Schema | Description ---------+---------+------------+------------------------------ plpgsql | 1.0 | pg_catalog | PL/pgSQL procedural language (1 row)

To get a list of available extensions, we can query the pg_available_extensions view, as shown here:

postgres=# SELECT name,comment FROM pg_available_extensions limit 5; name | comment ----------+-------------------------------------------------------------- dblink | connect to other PostgreSQL databases from within a database isn | data types for international product numbering standards file_fdw | foreign-data wrapper for flat file access tsearch2 | compatibility package for pre-8.3 text search functions unaccent | text search dictionary that removes accents (5 rows)

Let's try installing one extension and then see the list of installed extensions again:

postgres=# CREATE EXTENSION dblink ; CREATE EXTENSION postgres=# \dx List of installed extensions Name | Version | Schema | Description ---------+---------+------------+-------------------------------------------------------------- dblink | 1.1 | public | connect to other PostgreSQL databases from within a database plpgsql | 1.0 | pg_catalog | PL/pgSQL procedural language (2 rows)

The dblink extension has been added to the list of installed extensions. To remove it, just drop it:

postgres=# DROP EXTENSION dblink ; DROP EXTENSION postgres=# \dx List of installed extensions Name | Version | Schema | Description ---------+---------+------------+------------------------------ plpgsql | 1.0 | pg_catalog | PL/pgSQL procedural language (1 row)

Tip

Downloading the example code

You can download the example code files from your account at http://www.packtpub.com for all the Packt Publishing books you have purchased. If you purchased this book elsewhere, you can visit http://www.packtpub.com/support and register to have the files e-mailed directly to you.

Summary

In this chapter, we covered the steps to install PostgreSQL from the source: downloading, configuring, building and installing. We went through the directory structure of the source tree, the cluster initialization process, the resultant directories and files, as well as the process to install and remove extensions.

In the next chapter, we will cover PostgreSQL Server Architecture. We will cover the various background processes, their functions, memory structures and how they all work with each other to provide the many features available in PostgreSQL.