Ash: We definitely don't run thousands of tasks. Looks like it's closer to 300 per execution date (and then retries), if I'm using the TI browser right.
In my case, I found 21 tasks in "scheduled" state after 1 day of not restarting. One of our hourly "canary" DAGs got included in the pile-up - so it didn't run that hour as expected, so I got paged. (But it wasn't just canary tasks, the other 20 tasks were all real and important workflows that were not getting scheduled.) If we do change the scheduler to have a "cleanup" step within the loop instead of pre/post loop, I'd suggest we should: - Make the time between cleanups a configurable parameter - Log what cleanup steps are being taken and how long they take - Add new statsd metrics around cleanups (like "number of orphans reset"), to help us understand when and why this happens On Wed, Jul 31, 2019 at 1:25 PM Tao Feng <fengta...@gmail.com> wrote: > Late in the game as I was't aware of `run_duration` option been removed. > But just want to point out that Lyft also did very similar with James' > setup that we run the scheduler in a fix internal instead of infinite loop > and let the runit/supervisor to restart the scheduler process. This is to > solve: 1. orphaned tasks not getting clean up successfully when it runs on > infinite loop; 2. Make sure stale / deleted DAG will get clean up( > > https://github.com/apache/airflow/blob/master/airflow/jobs/scheduler_job.py#L1438 > ? > <https://github.com/apache/airflow/blob/master/airflow/jobs/scheduler_job.py#L1438?> > ) > properly. > > I think if it goes with removing this option and let scheduler runs in an > infinite loop, we need to change the schedule loop to handle the clean up > process if it hasn't been done. > > On Wed, Jul 31, 2019 at 10:10 AM Ash Berlin-Taylor <a...@apache.org> wrote: > > > Thanks for testing this out James, shame to discover we still have > > problems in that area. Do you have an idea of how many tasks per day we > are > > talking about here? > > > > Your cluster schedules quite a large number of tasks over the day (in the > > 1k-10k range?) right? > > > > I'd say whatever causes a task to become orphaned _while_ the scheduler > is > > still running is the actual bug, and running the orphan detection more > > often may just be replacing one patch (the run duration) with another one > > (running the orphan detection more than at start up). > > > > -ash > > > > > On 31 Jul 2019, at 16:43, James Meickle <jmeic...@quantopian.com > .INVALID> > > wrote: > > > > > > In my testing of 1.10.4rc3, I discovered that we were getting hit by a > > > process leak bug (which Ash has since fixed in 1.10.4rc4). This process > > > leak was minimal impact for most users, but was exacerbated in our case > > by > > > using "run_duration" to restart the scheduler every 10 minutes. > > > > > > To mitigate that issue while remaining on the RC, we removed the use of > > > "run_duration", since it is deprecated as of master anyways: > > > > > > https://github.com/apache/airflow/blob/master/UPDATING.md#remove-run_duration > > > > > > Unfortunately, testing on our cluster (1.10.4rc3 plus no > "run_duration") > > > has revealed that while the process leak issue was mitigated, that > we're > > > now facing issues with orphaned tasks. These tasks are marked as > > > "scheduled" by the scheduler, but _not_ successfully queued in Celery > > even > > > after multiple scheduler loops. Around ~24h after last restart, we > start > > > having enough stuck tasks that the system starts paging and requires a > > > manual restart. > > > > > > Rather than generic "scheduler instability", this specific issue was > one > > of > > > the reasons why we'd originally added the scheduler restart. But it > > appears > > > that on master, the orphaned task detection code still only runs on > > > scheduler start despite removing "run_duration": > > > > > > https://github.com/apache/airflow/blob/master/airflow/jobs/scheduler_job.py#L1328 > > > > > > Rather than immediately filing an issue I wanted to inquire a bit more > > > about why this orphan detection code is only run on scheduler start, > > > whether it would be safe to send in a PR to run it more often (maybe a > > > tunable parameter?), and if there's some other configuration issue with > > > Celery (in our case, backed by AWS Elasticache) that would cause us to > > see > > > orphaned tasks frequently. > > > > >
