更新`djcelery_periodictask`表时的死锁

Question

我有两个简单的周期性芹菜任务在晚上运行，一个在凌晨2点，另一个在凌晨3点，然后从时间上抛出关于djcelery_periodictask表上的死锁的异常(我不太理解)。似乎有一个任务试图更新djcelery_periodictask，而另一个任务仍然持有共享锁：

deadlock detected Detail: Process 32353 waits for ShareLock on transaction 39280165; blocked by process 32306. Process 32306 waits for ShareLock on transaction 39280166; blocked by process 32353. 
Process 32353: 
UPDATE "djcelery_periodictask" SET "name" = 'app.tasks.task1', "task" = 'app.tasks.task1', "interval_id" = NULL, "crontab_id" = 4, "args" = '[]', "kwargs" = '{}', "queue" = NULL, "exchange" = NULL, "routing_key" = NULL, "expires" = NULL, "enabled" = true, "last_run_at" = '2015-02-10 03:00:00.001297+01:00', "total_run_count" = 117, "date_changed" = '2015-02-10 02:00:00.010033+00:00', "description" = '' WHERE "djcelery_periodictask"."id" = 4 
Process 32306: 
UPDATE "djcelery_periodictask" SET "name" = 'app.tasks.task2', "task" = 'app.tasks.task2', "interval_id" = NULL, "crontab_id" = 6, "args" = '[]', "kwargs" = '{}', "queue" = NULL, "exchange" = NULL, "routing_key" = NULL, "expires" = NULL, "enabled" = true, "last_run_at" = '2015-02-10 02:00:00.014189+01:00', "total_run_count" = 63, "date_changed" = '2015-02-10 02:00:00.015097+00:00', "description" = '' WHERE "djcelery_periodictask"."id" = 6 
Hint: See server log for query details. Query: 
UPDATE "djcelery_periodictask" SET "name" = 'app.tasks.task2', "task" = 'appt.tasks.task2', "interval_id" = NULL, "crontab_id" = 4, "args" = '[]', "kwargs" = '{}', "queue" = NULL, "exchange" = NULL, "routing_key" = NULL, "expires" = NULL, "enabled" = true, "last_run_at"

这两个简单的更新怎么会导致死锁呢？

Answer 1

我的问题是，我让我的所有工作人员从-B参数开始，该参数将每个工作人员转换为一个定期任务调度程序：

-B, --beat            Also run the celery beat periodic task scheduler.
                      Please note that there must only be one instance of
                      this service.

结果，计划的任务被多次启动，所有这些任务都同时启动，在尝试更新djcelery_periodictask表时创建了一个死锁。