Getting lots of PG:: errors with Rails 3.2.16 (last major stable release) and ruby-pg 0.17.1 (up to date).

pg_errors.rb

require 'rubygems' rescue nil

gem 'activerecord', '3.2.16'
gem 'pg', '0.17.1'

require 'active_record'
require 'logger'

puts ActiveRecord::VERSION::STRING

db_config = {
  adapter: 'postgresql',
  host: 'localhost',
  port: 5432,
  database: 'db_test',
  username: ENV['USER'],
  password: '',
  pool: 5,
  timeout: 5000,
  encoding: 'UTF8'
}

ActiveRecord::Base.logger = Logger.new($stdout)

ActiveRecord::Base.establish_connection(db_config.merge(database: 'postgres', schema_search_path: 'public'))
ActiveRecord::Base.connection.create_database(db_config[:database]) rescue ActiveRecord::StatementInvalid
ActiveRecord::Base.establish_connection(db_config) # back to db_test to create the table and use it
puts "PostgreSQL #{ActiveRecord::Base.connection.send(:postgresql_version)}" # => PostgreSQL 90302

ActiveRecord::Migration.class_eval do
  create_table :posts, force: true do |t|
    t.string :title
    t.text :body
  end
end

class Post < ActiveRecord::Base
end

pid = fork do
  ActiveRecord::Base.establish_connection(db_config) # my mother said I never should keep using a db connection after a fork
  keep_going = true
  Signal.trap('HUP') { keep_going = false }
  while keep_going
    Post.where(title: 'Subprocess').first_or_create
  end
end

#ActiveRecord::Base.connection.reconnect! # Riddle me this: why is this necessary? why does this make it work?

begin
  20000.times do
    ActiveRecord::Base.connection.execute('TRUNCATE posts CASCADE')
    Post.where(title: 'Main').first_or_create
    # activerecord-3.2.16/lib/active_record/connection_adapters/postgresql_adapter.rb:1163:in `async_exec': PG::ConnectionBad: PQconsumeInput() :             SELECT a.attname, format_type(a.atttypid, a.atttypmod), (ActiveRecord::StatementInvalid)
    #                      pg_get_expr(d.adbin, d.adrelid), a.attnotnull, a.atttypid, a.atttypmod
    #               FROM pg_attribute a LEFT JOIN pg_attrdef d
    #                 ON a.attrelid = d.adrelid AND a.attnum = d.adnum
    #              WHERE a.attrelid = '"posts"'::regclass
    #                AND a.attnum > 0 AND NOT a.attisdropped
    #              ORDER BY a.attnum
  end
ensure
  Process.kill('HUP', pid)
  Process.wait
end