begin

  # Get the hash (i.e. parsed) representation of database.yml
  databases = Rails.configuration.database_configuration
  
  # Get a fancier AR-specific representation of database.yml
  resolver = ActiveRecord::ConnectionAdapters::ConnectionSpecification::Resolver.new(databases)
  
  # Get one specific database from our list of databases in database.yml. pick any database identifier (:development, :user_shard1, etc)
  spec = resolver.spec(:development)
  
  # Make a new pool for the database we picked
  pool = ActiveRecord::ConnectionAdapters::ConnectionPool.new(spec)
  
  # Use the pool
  # This is thread-safe, ie unlike ActiveRecord's establish_connection, it won't leak to other threads
  pool.with_connection {
    puts Post.count
  }
  
rescue => ex
  puts ex, ex.backtrace
ensure
  pool.disconnect!
end