气流在首次打开时启动两次DAG运行 [英] Airflow starts two DAG runs when turned on for the first time

问题描述

当我在10月25日17:23左右首次启动Airflow Web服务器和调度程序并打开DAG时，我可以看到它在10月23日和10月24日开始了两次运行：

  RUN 1-> 10-23T17：23 
 RUN 2-> 10-24T17：23 
  

这是我的DAG配置：

  default_args = {
'所有者'：'气流'，
'depends_on_past'：否，
'起始日期'：'2019-01 -01'，
'重试'：0，
} 
 dag = DAG（
'my_script'，
 default_args = default_args，
 schedule_interval = datetime .timedelta（days = 1），
 catchup = False，
）
  

由于已经过去了 start_date + schedule_interval ，并且我已经设置了 catchup = False ，所以我希望它会启动一个DAG立即运行，但是我不希望它运行两次。

• 为什么要执行两次DAG运行？


• 如何防止这种行为？

解决方案

我不确定，但是这是我最好的猜测-

简而言之，可能是气流的建立方式，解决方法是修改您的开始日期 t

TL; DR

我同意当您开始10到24天的1 dag打开听起来更自然。

但是，根据您的数据，运行1是10-23。
这向我表明，第一次运行的初始化是不正确的，我已经研究了调度程序代码。

我对此行有疑问。

https://github.com/apache/airflow/blob/68b8ec5f415795e4fa4ff7df35a3e75c712a7bad/airflow/jobs/scheduler_job.py#L603

这是内部

  ##逻辑是我们将start_date向上移动到
＃一个周期之前，因此timezone.utcnow（）在
＃期末之后，可以创建作业... 
现在= timezone.utcnow（）
 
＃返回当前时间+ schedule_interval。在您的示例中，这将是明天。 
 next_start = dag.following_schedule（now）
 
＃返回当前时间-schedule_interval。在您的示例中，这将是昨天。 
 last_start = dag.previous_schedule（now）
 
＃明天< =今天应该返回False 
如果next_start< =现在：
 new_start = last_start 
 else：
＃，这将返回last_start-schedule_interval，表示2天前。 
＃想知道这是否是dag.previous_schedule（next_start）??? 
 new_start = dag.previous_schedule（last_start）
  

When I boot up the Airflow webserver and scheduler for the first time on Oct 25th at around 17:23, and turn on my DAG, I can see that it kicks off two runs for Oct 23rd and Oct 24th:

RUN 1 -> 10-23T17:23
RUN 2 -> 10-24T17:23

Here's my DAG configuration:

default_args = {
    'owner': 'airflow',
    'depends_on_past': False,
    'start_date': '2019-01-01',
    'retries': 0,
}
dag = DAG(
    'my_script',
    default_args=default_args,
    schedule_interval=datetime.timedelta(days=1),
    catchup=False,
)

Since it's past the start_date + schedule_interval and I have set catchup=False, I would expect it to kick off a single DAG run immediately, however I would not expect it to run two.

• Why are two DAG runs being executed?
• How can I prevent this behaviour?

解决方案

I am not sure but this is my best guess -

In short answer, could be it is how airflow is built and workaround would be to modify your start_date to be yesterday.

TL;DR

I agree that kicks off 1 dag for 10-24 when you turned on would sound more natural.

However, according to your dag runs, RUN 1 is 10-23. This suggests to me that initializing of the first run is not correct and I have looked into the scheduler code.

And I have a doubt on this line.

https://github.com/apache/airflow/blob/68b8ec5f415795e4fa4ff7df35a3e75c712a7bad/airflow/jobs/scheduler_job.py#L603

This is inside a function that create a dag run and setting the start date of the run.

# The logic is that we move start_date up until
# one period before, so that timezone.utcnow() is AFTER
# the period end, and the job can be created...
now = timezone.utcnow()

# This returns current time + schedule_interval. In your example, this will be tomorrow.
next_start = dag.following_schedule(now)

# This returns current time - schedule_interval. In your example, this will be yesterday.
last_start = dag.previous_schedule(now)

# tomorrow <= today should return False 
if next_start <= now:
    new_start = last_start
else:
    # and this will return last_start - schedule_interval which means 2 days ago.  
    # wondering if this is intended to be dag.previous_schedule(next_start)???
    new_start = dag.previous_schedule(last_start) 

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