Just a Theory

By David E. Wheeler


For years, I’ve managed multiple versions of PostgreSQL by regularly editing and running a simple script that builds each major version from source and installs it in /usr/local. I would shut down the current version, remove the symlink to /usr/local/pgsql, symlink the one I wanted, and start it up again.

This is a pain in the ass.

Recently I wiped my work computer (because reasons) and started reinstalling all my usual tools. PostgreSQL, I decided, no longer needs to run as the postgres user from /usr/local. What would be much nicer, when it came time to test pgTAP against all supported versions of Postgres, would be to use a tool like plenv or rbenv to do all the work for me.

So I wrote pgenv. To use it, clone it into ~/.pgenv (or wherever you want) and add its bin directories to your $PATH environment variable:

git clone https://github.com/theory/pgenv.git
echo 'export PATH="$HOME/.pgenv/bin:$HOME/.pgenv/pgsql/bin:$PATH"' >> ~/.bash_profile

Then you’re ready to go:

pgenv build 10.4

A few minutes later, it’s there:

$ pgenv versions

Let’s use it:

$ pgenv use 10.4
The files belonging to this database system will be owned by user "david".
This user must also own the server process.
#    (initdb output elided)
waiting for server to start.... done
server started
PostgreSQL 10.4 started

Now connect:

$ psql -U postgres
psql (10.4)
Type "help" for help.


Easy. Each version you install – as far back as 8.0 – has the default super user postgres for compatibility with the usual system-installed version. It also builds all contrib modules, including PL/Perl using /usr/bin/perl.

With this little app in place, I quickly built all the versions I need. Check it out:

$ pgenv versions
  *  pgsql-10.4

Other commands include start, stop, and restart, which act on the currently active version; version, which shows the currently-active version (also indicated by the asterisk in the output of the versions command); clear, to clear the currently-active version (in case you’d rather fall back on a system-installed version, for example); and remove, which will remove a version. See the docs for details on all the commands.

How it Works

All this was written in an uncomplicated Bash script. I’ve ony tested it on a couple of Macs, so YMMV, but as long as you have Bash, Curl, and /usr/bin/perl on a system, it ought to just work.

How it works is by building each version in its own directory: ~/.pgenv/pgsql-10.4, ~/.pgenv/pgsql-11beta2, and so on. The currently-active version is nothing more than symlink, ~/.pgenv/pgsql, to the proper version directory. There is no other configuration. pgenv downloads and builds versions in the ~/.pgenv/src directory, and the tarballs and compiled source left in place, in case they’re needed for development or testing. pgenv never uses them again unless you delete a version and pgenv build it again, in which case pgenv deletes the old build directory and unpacks from the tarball again.

Works for Me!

Over the last week, I hacked on pgenv to get all of these commands working. It works very well for my needs. Still, I think it might be useful to add support for a configuration file. It might allow one to change the name of the default superuser, the location Perl, and perhaps a method to change postgresql.conf settings following an initdb. I don’t know when (or if) I’ll need that stuff, though. Maybe you do, though? Pull requests welcome!

But even if you don’t, give it a whirl and let me know if you find any issues.

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