Rails 4多線程和connection_pool問題

Question

我正在嘗試對Rails應用程序進行多線程處理，但是遇到了connection_pool的一些問題。 我啟動一個線程並執行數據庫查詢，但是似乎從來沒有關閉該線程中創建的數據庫連接。 這是我的代碼：

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

當我執行10次{A.foo}時，它給出了這個輸出。

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

最后我跑了：

ActiveRecord::Base.connection_pool.connections.size
5

現在，根據文檔， with_connection應該包含一個塊並使用連接將其執行，然后關閉該連接，但是根據我的輸出，它沒有。 我真的不明白。

是否有人有任何解決方案或想法可能會發生這種情況？ 使用“ connection_pool.connections.size”是檢查多少個連接的正確方法嗎？

還有其他方法可以在Rails中實現多線程數據庫查詢嗎？

Answer 1

好的，所以我只是不了解connection_pool的工作方式。 連接池保存自創建該池以來已打開的連接，無論是否正在使用它們。 因此，我的問題的答案是，您（無法通過今天實現的方式）無法通過connection_pool查看正在積極使用的連接。 相反，我修補了連接池本身以包括此功能。

如果有人感興趣，這是我的補丁放在config / initializers / connection_pool_patch.rb中：

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

它公開了私有列表@available的大小，該私有列表在連接池中保存了可用（即，當前未使用但已打開）的連接。 用法= ActiveRecord :: Base.connection_pool.num_available