Rails 4多线程和connection_pool问题

Question

我正在尝试多线程我的rails应用程序，但是遇到了connection_pool的一些问题。我启动了一个线程并执行数据库查询，但在线程中创建的数据库连接似乎从未关闭过。这是我的代码：

class A
def self.foo
    Thread.new do
      nc1 = ActiveRecord::Base.connection_pool.connections.size
      nw = ""
      nc2 = ""

      ActiveRecord::Base.connection_pool.with_connection do |conns|
        nw = Person.count
        nc2 = ActiveRecord::Base.connection_pool.connections.size
      end

      nc3 = ActiveRecord::Base.connection_pool.connections.size
      puts "First there were #{nc1} connections, after things there were #{nc2} and now finally there are #{nc3} connections, there are #{nw} people in the db"  
    end
  end 
end

当我执行10.x {A.foo}时，它会给出以下输出。

First there were 1 connections, after things there were 3 and now finally there are 5 connections, there are 5325 people in the db
First there were 1 connections, after things there were 4 and now finally there are 5 connections, there are 5325 people in the db
First there were 1 connections, after things there were 2 and now finally there are 5 connections, there are 5325 people in the db
First there were 1 connections, after things there were 5 and now finally there are 5 connections, there are 5325 people in the db
First there were 1 connections, after things there were 5 and now finally there are 5 connections, there are 5325 people in the db
First there were 1 connections, after things there were 5 and now finally there are 5 connections, there are 5325 people in the db
First there were 1 connections, after things there were 5 and now finally there are 5 connections, there are 5325 people in the db
First there were 1 connections, after things there were 5 and now finally there are 5 connections, there are 5325 people in the db
First there were 1 connections, after things there were 5 and now finally there are 5 connections, there are 5325 people in the db
First there were 1 connections, after things there were 5 and now finally there are 5 connections, there are 5325 people in the db

最后我跑起来：

ActiveRecord::Base.connection_pool.connections.size
5

现在根据documentation的说法，with_connection应该通过一个连接来执行它，然后它会关闭，但是根据我的输出，它没有，我真的不明白。

有没有人有任何解决方案或想法，为什么会发生这种情况？使用"connection_pool.connections.size“是检查有多少连接的正确方式吗？

是否有其他方法可以在rails中实现多线程数据库查询？

Answer 1

好吧，我只是不理解connection_pool是如何工作的。连接池保存自创建池以来已打开的连接，无论它们是否正在使用。因此，我的问题的答案是，您无法(以目前的实现方式)通过connection_pool来查看哪些连接正在被活跃地使用。相反，我对连接池本身进行了修补，以包含此功能。

如果有人感兴趣，这是我在config/initializers/connection_pool_patch.rb中的补丁：

module ActiveRecord
  module ConnectionAdapters
    class ConnectionPool
      def num_available
        @available.size
      end
    end
  end
end

module ActiveRecord
  module ConnectionAdapters
    class ConnectionPool
      class Queue
        def size
          @queue.size
        end
      end
    end
  end
end

它暴露了私有列表@available的大小，该私有列表保存了连接池中可用(即当前未使用但已打开)的连接。用法= ActiveRecord::Base.connection_pool.num_available