redmine 糟糕的寫入性能（更新不是真正的多執行緒）

（已經自我回答）我正在與大約 100 個使用者的 redmine 性能不佳作鬥爭。為了測試它，我設置了一個簡單的場景來更新五個不同範例問題的“完成百分比”。所有更新都在同一秒開始，使用curl. 令我驚訝的是，redmine 中的更新似乎是序列化的（我的意思是不是多執行緒的），時序如下：

real    0m1.122s
real    0m1.404s
real    0m2.258s
real    0m2.782s
real    0m3.151s
real    0m3.336s

或者另一種嘗試，當其他會話的一些處理也受到阻礙時：

real    0m7.492s
real    0m7.803s
real    0m8.045s
real    0m8.246s
real    0m8.597s
real    0m8.825s

production.log在處理大量 SQL 查詢後的關鍵時刻是 COMMIT 階段。請注意 COMMIT 是如何在毫秒內完成的，但在 COMMIT 之間發生了一些神秘的事情，不僅將它們序列化，而且需要幾秒鐘才能達到 Completed 狀態。此日誌摘錄完好無損 - 我沒有刪除中間的任何行。

  (0.6ms)  SELECT COUNT(*) FROM `custom_workflows` WHERE `custom_workflows`.`active` = 1 AND `custom_workflows`.`observable` = 'issue' AND (is_for_all OR EXISTS (SELECT * FROM custom_workflows_projects WHERE project_id=123 AND custom_workflow_id=id))
  (30.1ms)  COMMIT
Redirected to http://redmine.mydomain.local/issues/11973
Completed 302 Found in 7418.4ms (ActiveRecord: 135.8ms)
  (0.6ms)  SELECT COUNT(*) FROM `custom_workflows` WHERE `custom_workflows`.`active` = 1 AND `custom_workflows`.`observable` = 'issue' AND (is_for_all OR EXISTS (SELECT * FROM custom_workflows_projects WHERE project_id=123 AND custom_workflow_id=id))
  (24.8ms)  COMMIT
Redirected to http://redmine.mydomain.local/issues/9240
Completed 302 Found in 7738.3ms (ActiveRecord: 57.4ms)
  (0.4ms)  SELECT COUNT(*) FROM `custom_workflows` WHERE `custom_workflows`.`active` = 1 AND `custom_workflows`.`observable` = 'issue' AND (is_for_all OR EXISTS (SELECT * FROM custom_workflows_projects WHERE project_id=123 AND custom_workflow_id=id))
  (25.9ms)  COMMIT
Redirected to http://redmine.mydomain.local/issues/9614
Completed 302 Found in 7949.0ms (ActiveRecord: 135.7ms)
  (0.5ms)  SELECT COUNT(*) FROM `custom_workflows` WHERE `custom_workflows`.`active` = 1 AND `custom_workflows`.`observable` = 'issue' AND (is_for_all OR EXISTS (SELECT * FROM custom_workflows_projects WHERE project_id=123 AND custom_workflow_id=id))
  (24.6ms)  COMMIT
Redirected to http://redmine.mydomain.local/issues/12016
Completed 302 Found in 8058.5ms (ActiveRecord: 102.5ms)
  (0.5ms)  SELECT COUNT(*) FROM `custom_workflows` WHERE `custom_workflows`.`active` = 1 AND `custom_workflows`.`observable` = 'issue' AND (is_for_all OR EXISTS (SELECT * FROM custom_workflows_projects WHERE project_id=123 AND custom_workflow_id=id))
  (21.2ms)  COMMIT
Redirected to http://redmine.mydomain.local/issues/8853
Completed 302 Found in 8472.5ms (ActiveRecord: 90.4ms)
  (0.5ms)  SELECT COUNT(*) FROM `custom_workflows` WHERE `custom_workflows`.`active` = 1 AND `custom_workflows`.`observable` = 'issue' AND (is_for_all OR EXISTS (SELECT * FROM custom_workflows_projects WHERE project_id=123 AND custom_workflow_id=id))
  (27.9ms)  COMMIT
Redirected to http://redmine.mydomain.local/issues/10007
Completed 302 Found in 8700.4ms (ActiveRecord: 137.4ms)

我已經檢查過的內容：

• 乘客狀態的執行緒數綽綽有餘
• apache2 httpd 的程序數綽綽有餘
• mysql 5.1 使用 innodb
• innotop 不顯示鎖
• innotop 不會過多的 I/O
• iostat 沒有顯示過多的 I/O（大約 10-15 IOPS，磁碟最大 17% 的時間使用）
• top 沒有顯示過多的 CPU 使用率（最多可能 400% 的 70%）。

好的，這是 SMTP 序列化的東西；預設情況下它以某種方式未記錄。

我改變了/var/www/html/redmine/config/configuration.yml：

 email_delivery:
   # delivery_method: :smtp       # slows down everything!
   delivery_method: :async_smtp

引用自：https://serverfault.com/questions/759752