Rails 3.1 - Pushing to Heroku - Errors installing postgres adapter?

Question

I just upgraded to Rails 3.1 and the first app i've tried to deploy to Heroku has encountered a problem relating to Postgres adapter. I'm able to push the app to heroku but then when i try to migrate the database i get the following error:

heroku rake db:migrate

rake aborted!
Please install the postgresql adapter: `gem install activerecord-postgresql-adapter` 
(pg is not part of the bundle. Add it to Gemfile.)
Tasks: TOP => db:migrate => db:load_config
(See full trace by running task with --trace)

when I try their suggested install i get:

ERROR:  Could not find a valid gem 'activerecord-postgresql-adapter' (>= 0) in any repository
ERROR:  Possible alternatives: activerecord-postgis-adapter, activerecord-jdbcpostgresql-adapter, activerecord-postgresql-cursors, activerecord-jdbcmysql-adapter, activerecord-jdbcmssql-adapter

which already seems weird... so what exact gem should I install to get this thing working if not what they say I should install??

When I try installing gem pg i get:

Building native extensions.  This could take a while...
ERROR:  Error installing pg:
        ERROR: Failed to build gem native extension.

/Users/jerometufte/.rvm/rubies/ruby-1.9.2-p180/bin/ruby extconf.rb
checking for pg_config... no
No pg_config... trying anyway. If building fails, please try again with
 --with-pg-config=/path/to/pg_config
checking for libpq-fe.h... no
Can't find the 'libpq-fe.h header
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of
necessary libraries and/or headers.  Check the mkmf.log file for more
details.  You may need configuration options.

Provided configuration options:
    --with-opt-dir
    ...

I'm using SQLite3 currently. Any help greatly appreciated, this is baffling me.

Answer 1

Option 1:

Add pg to your Gemfile but skip trying to install it locally.

$ cat Gemfile
...
group :production do
  # gems specifically for Heroku go here
  gem "pg"
end

# Skip attempting to install the pg gem
$ bundle install --without production

Option 2 (Debian/Ubuntu):

Add pg to your Gemfile but first install the prerequisites.

$ cat Gemfile
...
group :production do
  # gems specifically for Heroku go here
  gem "pg"
end

# Install the pg gem's dependencies first
$ sudo apt-get install libpq-dev
# Then install the pg gem along with all the other gems
$ bundle install