After upgrading PostgreSQL from 8.4 to 9.1 pg gem doesn't connect to the database

Question

As the title says, I've upgraded the PostgreSQL database from version 8.4 to 9.1.

My pg_hba.conf file contains following:

local   all        all            trust

# TYPE  DATABASE        USER            ADDRESS                 METHOD

# "local" is for Unix domain socket connections only
#local   all             all                                     md5
# IPv4 local connections:
host    all             all             127.0.0.1/32            md5
# IPv6 local connections:
host    all             all             ::1/128                 md5

I also ran these commands:

sudo gem uninstall pg
sudo apt-get remove libpq-dev
sudo apt-get install libpq-dev
sudo gem install pg
sudo service postgresql restart

When I run psql from the command line all works properly, but here's what happens when I try to connect from the Ruby console:

$:  /va$ sudo pry
[1] pry(main)> require 'pg'
=> true
[2] pry(main)> conn = PG.connect( dbname: 'mydb' )
PG::ConnectionBad: could not connect to server: No such file or directory
        Is the server running locally and accepting
        connections on Unix domain socket "/var/run/postgresql/.s.PGSQL.5432"?
from /usr/local/lib/ruby/gems/1.9.1/gems/pg-0.17.1/lib/pg.rb:40:in `initialize'

Answer 1

Your Pg gem is using a libpq version that defaults to a different unix_socket_directory to the one your new server uses. Most likely your new server uses /tmp and your old one used /var/run/postgresql.

You can force a TCP/IP connection by specifying localhost as the target host to connect to, e.g a connstring like dbname=fred host=localhot user=bob, or however you're giving the parameters to the Pg gem. That's not really the best answer, though.

Instead, you should either:

• Rebuild the pg gem against the updated libpq from your new PostgreSQL install. To do that, set PATH so that the pg_config from the new PostgreSQL install is first on the path before rebuilding the Pg gem. You can check the version with pg_config --version.

or

• Specify the unix_socket_directory to connect to explicitly, with host=/tmp dbname=fred user=bob. The host parameter can take a hostname or a path to a socket directory. Doing this means you're still using nice efficient unix sockets for your sessions and not paying unnecessary TCP/IP overheads.