a_program.rb

query_factory = MemoizingQueryFactory.new(TimingOutQueryFactory.new(Query, 1.second))
QueryEvaluator.new(ConnectionPool.new(20), query_factory)

memoizing_query_factory.rb

class MemoizingQueryFactory
  def initialize(query_factory)
    @memo = Hash.new do |h, k|
      h = query_factory.new(*k)
    end
  end

  def new(connection, query_string, *args)
    @memo[[connection, query_string, args]]
  end
end

query_evaluator.rb

class QueryEvaluator
  def initialize(connection_pool, query_factory = Query)
    @query_factory = query_factory
    @connection_pool = connection_pool
  end

  def select(query_string, *args)
    @connection_pool.with_connection do |connection|
      @query_factory.new(connection, query_string, *args).select
    end
  end
end

timing_out_query_proxy.rb

class TimingOutQueryProxyFactory
  def initialize(query_factory, timeout)
    @query_factory = query_factory
    @timeout = timeout
  end

  def new(connection, query_string, *args)
    @query_factory.new(connection, query_string, *args)
  end
end

class TimingOutQueryProxy
  def initialize(query, timeout)
    @query = query
    @timeout = timeout
  end

  def select
    Timeout.timeout(@timeout) do
      @query.select
    end
  end

  # ...
end