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Re: Fundamental change - Separate DAG name and id.


Re: [Brian Greene] "How does filename matter?  Frankly I wish the filename
was REQUIRED to be the dag name so people would quit confusing themselves
by mismatching them !"

FWIW in the Facebook predecessor to airflow, the file path/name WAS the dag
name. E.g. if your dag resided in best_team/new_project/sweet_dag.py then
the dag name would be best_team.new_project.sweet_dag
All tasks were identified by their variable name after that prefix: E.g. if
best_team.new_project.sweet_dag defines an operator in a variable named
task1, then the respective task_id is best_team.new_project.sweet_dag.task1.

Airflow provides additional flexibility to specify DAG and task names to
avoid the sometimes annoyingly long task names this resulted in and allow
DAG/task names without forcing a code directory structure and python's
variable naming restrictions, and I think this is a Good Thing.

It seems like airflowuser is trying to provide additional metadata beyond
the DAG/task names (so far, a DAG 'title' distinct from the ID). I've
provided this through a README.md included in the DAG source directory, but
maybe it would be a win to instead add a DAG parameter named 'readme' of
string type which can include a docstring or even markdown to provide any
desired additional metadata? This could then be displayed by the UI to
simplify access to any such provided DAG documentation.

🍿



On Thu, Sep 20, 2018 at 10:45 PM Brian Greene <
brian@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

> Prior to using airflow for much, on first inspection, I think I may have
> agreed with you.
>
> After a bit of use I’d agree with Fokko and others - this isn’t really a
> problem, and separating them seems to do more harm than good related to
> deployment.
>
> I was gonna stop there, but why?
>
> You can add a task to a dag that’s deployed and has run and still view
> history.  The “new” task shows up white Squares in the old dags.  nobody
> said you’re required to also rename the dag when you do so this.  If your
> process or desire or design determines you need to rename it, well then by
> definition... isn’t it a new thing without a history?  Airflow is
> implementing exactly that.
>
> One could argue that renaming to reflect exact purpose is good practice.
> Yes, I’d agree, but again following that logic if it’s a small enough
> change to “slip in” then the name likely shouldn’t change.  If it’s big
> enough I want to change the name then it’s a big enough change that I’m
> functionally running something “new”, and I expect to need to account for
> that.  Airflow is enforcing that logic by coupling the name to the
> deployment of what you said was a new process.
>
> One might put forth that changing the name to be more descriptive In the
> ui makes it easier for support staff.  I think perhaps if that’s your
> challenge it’s not airflow that’s a problem.  Dags are of course documented
> elsewhere besides their name, right?  Yeah it’s self documenting (and the
> graphs are cool), but I have to assume there’s something besides the NAME
> to tell people what it does.  Additionally, far more than the name is
> required for even an operator or monitor watcher to take action - you don’t
> expect them to know which tasks to rerun or how to troubleshoot failures
> just based on your “now most descriptive name in the UI” do you?
>
> I spent time In an informatica shop where all the jobs were numbered.
> Numbered.  Let’s be more exact... their NAMES were NUMBERS like 56709.
> Terrible, but 100% worked, because while a descriptive name would have been
> useful, the name is the thing that’s supposed to NOT CHANGE (see code of
> Abibarshim), and all the other information can attach to that in places
> where you write... other information.  People would curse a number “F’ing
> 6291 failed again” - everyone knew what they were talking about.. I digress.
>
>  You might decide to document “dag ID 12” or just “12” on your wiki - I’m
> going to document “daily_sales_import”.  And when things start failing at
> 3am it’s not my dag “56” that’s failing, it’s the sales_export dag.  But if
> you document “12”, that’s still it’s name, and it’d better be 12 in all
> your environments and documents.  This also means the actual db IDs from
> your proposal are almost certainly NOT the same across your environments,
> making the 12 unchangeable name!
>
> There are lots of languages (most of them) where the name of a thing is
> important and hard to change.  It’s not a bad thing, and I’d assume that
> deploying a thing by name has some significance in many systems.  Go rename
> a class in... pick a language... tell me how that should be easier to do
> willy-nilly so it’s easier In the UI.
>
> I suppose you could view it as a limitation, But i don’t think you’ve
> illuminated a single use case where it’s an actual technical constraint or
> limitation.
>
> The BEST argument against the current implementation is db performance.
> It’s a hogwash argument.  Basic key indexes on low cardinality string
> columns are plenty fast for the airflow workload, and if your task load is
> so high airflow can’t keep up or your seeing super-fast tasks and airflow
> db/tracking latency is too much... perhaps a messaging or queue processing
> solution is better suited to those workloads.  We see scheduler bottlenecks
> long before the database for our “quick task” scenarios.  Additionally,
> reading through this list you’ll find people running airflow at substantial
> scale - I’ve not seen anyone complaining of production performance issues
> based on this design decision.   At first I hated it.  String keys are
> dirty, we’re all taught that as good little programmers.  Except when
> performance won’t be a huge consideration since it’s not OLTP and easy of
> queryabilty is more important because it’s a growing system... good
> decision - whoever made it.
>
> How does filename matter?  Frankly I wish the filename was REQUIRED to be
> the dag name so people would quit confusing themselves by mismatching them
> !   We’ve renamed dag files with no issue as long as the content doesn’t
> change, so again, not a real use case.  And really - name your stuff
> careful before you get to prod man.
>
> I gotta ask - airflowuser - are you gonna use airflow for anything, or
> just poke it with a stick from a distance and ask semi-inane questions of
> these fine folks that wrote and spend time working on this cool piece of
> kit?
>
> B
>
> Sent from a device with less than stellar autocorrect
>
> > On Sep 20, 2018, at 3:12 PM, Driesprong, Fokko <fokko@xxxxxxxxxxxxxx>
> wrote:
> >
> > I like the dag_id for both the name and as an unique identifier. If you
> > change the dag in such a way, that it deserves a new name, you probably
> > want to create a new dag anyway. If you want to give some additional
> > context, you can use the description field:
> >
> https://github.com/apache/incubator-airflow/blob/master/airflow/models.py#L3131-L3132
> >
> > The name of the file of dag does not have any influence.
> >
> > My 2¢
> >
> > Cheers, Fokko
> >
> > Op do 20 sep. 2018 om 19:40 schreef James Meickle
> > <jmeickle@xxxxxxxxxxxxxx.invalid>:
> >
> >> I'm personally against having some kind of auto-increment numeric ID for
> >> DAGs. While this makes a lot of sense for systems where creation is a
> >> database activity (like a POST request), in Airflow, DAG creation is
> >> actually a code ship activity. There are all kinds of complex scenarios
> >> around that:
> >>
> >> - I revert a commit and a DAG disappears or is renamed
> >> - I run the same file, twice, with multiple parameters to create two
> DAGs
> >> - I create the DAG in both staging and prod, but they wind up with
> >> different IDs
> >>
> >> It's just too hard to automatically track these scenarios.
> >>
> >> If we really wanted to put something like this in place, it would first
> >> make more sense to decouple DAG creation from code shipping, and instead
> >> prefer creation of a DAG outside of code (but with a definition that
> >> references which git repo/committish/file/arguments/etc. to use). Then
> if
> >> you do something like rename a file, the DAG breaks, but at least still
> >> exists in the db with that ID and history still makes sense once you
> update
> >> the DAG definition with the new code location.
> >>
> >> On Thu, Sep 20, 2018 at 4:52 AM airflowuser
> >> <airflowuser@xxxxxxxxxxxxxx.invalid> wrote:
> >>
> >>> Hi,
> >>> though this could have been explained on Jira I think this should be
> >>> discussed first.
> >>>
> >>> The problem:
> >>> Airflow mixes DAG name with id. It uses same filed for both purposes.
> >>>
> >>> I assume that most of you use the dag_id to describe what the DAG
> >> actually
> >>> does.
> >>> For example:
> >>>
> >>> dag = DAG(
> >>>    dag_id='cost_report_daily',
> >>> ...
> >>> )
> >>>
> >>> This dag_id is reflected to the dag id column in the UI.
> >>> Now, lets say that you want to add another task to this specific dag -
> >> You
> >>> are to be extremely careful when you change the dag_id to represent the
> >> new
> >>> functionality for example : dag_id='cost_expenses_reports_daily' . This
> >>> will break the history of the DAG.
> >>>
> >>> Or even with simpler use case.. the user just want to change the name
> he
> >>> sees on the UI.
> >>>
> >>> I suggest to have a discussion if the dag_id should be split into id
> (an
> >>> actual id) and name to reflect what it does. When the "connection" is
> >> done
> >>> by id's  - names can change as much as you want without breaking
> >> anything.
> >>> essentially it becomes a field uses for display purpose  only.
> >>>
> >>> * I didn't mention also the issue of DAG file name which can also cause
> >>> trouble if someone wants to change it.
> >>>
> >>> Sent with [ProtonMail](https://protonmail.com) Secure Email.
> >>
>