I'm not sure I totally agree it's just a UI concept. I use the subdag operator to simplify dependencies too. If you have a group of tasks that need to finish before another group of tasks start, using a subdag is a pretty quick way to set those dependencies and I think also make it easier to follow the dag code.
On Fri, Jun 12, 2020 at 9:53 AM Kyle Hamlin <hamlin...@gmail.com> wrote: > I second Ash’s grouping concept. > > On Fri, Jun 12, 2020 at 5:10 AM Ash Berlin-Taylor <a...@apache.org> wrote: > > > Question: > > > > Do we even need the SubDagOperator anymore? > > > > Would removing it entirely and just replacing it with a UI grouping > > concept be conceptually simpler, less to get wrong, and closer to what > > users actually want to achieve with subdags? > > > > With your proposed change, tasks in subdags could start running in > > parallel (a good change) -- so should we not also just _enitrely_ remove > > the concept of a sub dag and replace it with something simpler. > > > > Problems with subdags (I think. I haven't used them extensively so may > > be wrong on some of these): > > - They need their own dag_id, but it has(?) to be of the form > > `parent_dag_id.subdag_id`. > > - They need their own schedule_interval, but it has to match the parent > dag > > - Sub dags can be paused on their own. (Does it make sense to do this? > > Pausing just a sub dag would mean the sub dag would never execute, so > > the SubDagOperator would fail too. > > - You had to choose the executor to operator a subdag with -- always a > > bit of a kludge. > > > > Thoughts? > > > > -ash > > > > On Jun 12 2020, at 12:01 pm, Ash Berlin-Taylor <a...@apache.org> wrote: > > > > > Workon sub-dags is much needed, I'm excited to see how this progresses. > > > > > > > > >> - *Unpack SubDags during dag parsing*: This rewrites the > > *DagBag.bag_dag* > > >> method to unpack subdag while parsing, and it will give a flat > > >> structure at > > >> the task level > > > > > > The serialized_dag representation already does this I think. At least > if > > > I've understood your idea here correctly. > > > > > > -ash > > > > > > > > > On Jun 12 2020, at 9:51 am, Xinbin Huang <bin.huan...@gmail.com> > wrote: > > > > > >> Hi everyone, > > >> > > >> Sending a message to everyone and collect feedback on the AIP-34 on > > >> rewriting SubDagOperator. This was previously briefly mentioned in the > > >> discussion about what needs to be done for Airflow 2.0, and one of the > > >> ideas is to make SubDagOperator attach tasks back to the root DAG. > > >> > > >> This AIP-34 focuses on solving SubDagOperator related issues by > > reattaching > > >> all tasks back to the root dag while respecting dependencies during > > >> parsing. The original grouping effect on the UI will be achieved > through > > >> grouping related tasks by metadata. > > >> > > >> This also makes the dag_factory function more reusable because you > don't > > >> need to have parent_dag_name and child_dag_name in the function > > signature > > >> anymore. > > >> > > >> Changes proposed: > > >> > > >> - *Unpack SubDags during dag parsing*: This rewrites the > > *DagBag.bag_dag* > > >> method to unpack subdag while parsing, and it will give a flat > > >> structure at > > >> the task level > > >> - *Simplify SubDagOperator*: The new SubDagOperator acts like a > > >> container and most of the original methods are removed. The > > >> signature is > > >> also changed to *subdag_factory *with *subdag_args *and > > *subdag_kwargs*. > > >> This is similar to the PythonOperator signature. > > >> - *Add a TaskGroup model and add current_group & parent_group > > attributes > > >> to BaseOperator*: This metadata is used to group tasks for > > >> rendering at > > >> UI level. It may potentially extend further to group arbitrary tasks > > >> outside the context of subdag to allow group-level operations (i.e. > > >> stop/trigger a group of task within the dag) > > >> - *Webserver UI for SubDag*: Proposed UI modification to allow > > >> (un)collapse a group of tasks for a flat structure to pair with the > > first > > >> change instead of the original hierarchical structure. > > >> > > >> > > >> Please see related documents and PRs for details: > > >> AIP: > > >> > > > https://cwiki.apache.org/confluence/display/AIRFLOW/AIP-34+Rewrite+SubDagOperator > > >> > > >> Original Issue: https://github.com/apache/airflow/issues/8078 > > >> Draft PR: https://github.com/apache/airflow/pull/9243 > > >> > > >> Please let me know if there are any aspects that you agree/disagree > > >> with or > > >> need more clarification (especially the third change regarding > > TaskGroup). > > >> Any comments are welcome and I am looking forward to it! > > >> > > >> Cheers > > >> Bin > > >> > > > -- > Kyle Hamlin >
