pg_test.rb

require 'pg'
class Context
  attr_reader :connections
  def initialize
    @connections = {}
  end

  def connection
    @connections.fetch(Process.pid) { @connections[Process.pid] = PG.connect( dbname: 'test' ) }
  end

  def disconnect
    if @connections[Process.pid]
      @connections.delete(Process.pid).close
    end
  end
end

context = Context.new
def before_fork(context)
  context.disconnect
end
def after_fork(context)
end

p context.connection.exec( "SELECT current_database();" ).to_a

before_fork(context)
fork do
  after_fork(context)
  p context.connection.exec( "SELECT current_database();" ).to_a
end

sleep 5
p context.connection.exec( "SELECT current_database();" ).to_a