I implemented the first version of DAG serialization part in AIP-24: https://github.com/apache/airflow/pull/5701. Please take a look if you are interested @all. Thanks!
It contains almost all fields of DAGs and tasks in the serialization (an example of serialized DAG here: https://github.com/apache/airflow/blob/35e38f19b09646a0f85a2a7866a8d9aacc345252/tests/dags/test_dag_serialization.py#L100). So basically the webserver can still treat them as before. No webserver UI code change is needed. The benefit is that we can use it for 1.10.*. Of course, it is a short-term fix compared to many long-term proposals. It only contains serialization. I verified its usage in UI end-to-end by using the Async DAG Loader in https://github.com/apache/airflow/pull/5594. I split the DAG serialization out of 5594 since Async DAG Loader is an optional one. (I suddenly recall that if there are N webserver process + 1 async DAG loading process, it may solve webserver inconsistency problem??) On Wed, Jul 31, 2019 at 10:33 AM Tao Feng <fengta...@gmail.com> wrote: > hey Zhou, > > Great to see this happens and make it backward compatible. I will persist > DAG into DB is definitely needed. And it will make migration easier with a > lightweight approach. At Lyft we sometimes observe nondeterministic > increased scheduling delay once users add some dynamic generated large DAGs > with thousands of tasks. > > I will spend some time to look at your proposal more in more detail. But I > agree that this is the most important pain point that we should address. > And let me know if anything I could help to facilitate this. > > > On Mon, Jul 29, 2019 at 2:13 PM Zhou Fang <zhouf...@google.com.invalid> > wrote: > > > Thanks everyone for the discussion. The comments are very helpful. > > > > AIP-24 that we proposed here is really a short-term one to minimize the > > change for fast launch and compatibility. I agree with the benefits of > the > > long-term proposals. It would be great if AIP-24 can be a first step (if > we > > can agree with the basic serialization approach). Then we can gradually > > apply long-term fixes. > > > > I summarized a few long-term proposals (from Fokko and Ash) and added a > > 'timeline' in AIP-24 (make things more clear): > > > > *Terms* > > > > - (this) stringified DAG: a patch to current DAG that can be JSONified > > - (long-term) serialized DAG: a new serializable DAG class used by > > webserver/scheduler > > > > *Proposed timeline* > > > > 1. (this) JSON Serialization of DAGs > > 1. will be out with https://github.com/apache/airflow/pull/5594 > > > > 2. (this, optional) Asynchronous DAG loading in webserver > > 1. webserver process uses a background process to collect DAGs, > > solve scalability issue before DAG persistence in DB being out > > 2. webserver process itself does not need to restart every 30s to > > collect DAGs > > 3. will be out with https://github.com/apache/airflow/pull/5594 > > > > 3. (this) DAG persistence in DB for webserver > > 1. minimal Airflow code change > > 2. an optional feature enabled via configuration > > 3. rolled out with Airflow 1.10.5 > > > > 4. (this, optional) Using DAG cached in DB for scheduling > > > > 5. (long-term) Defining serialized DAG for webserver > > 1. this proposal keeps all fields of DAG/Operator, however, some > > fields are not used by webserver or scheduler > > 2. trimming these fields are easy, just providing a list of fields > to > > include or exclude (Sec 2.3): _serialize_object(x, visited_dags) > > =>_serialize_object(x, visited_dags, include=['foo'], > > exclude=['bar']) > > 3. we should carefully check all webserver/scheduler code to make > > sure trimmed fields are not used, e.g., *task.owner* is used in > > webserver > > > > 6. (long-term) Defining serialized DAG for scheduler > > 1. Once we have 'stringified DAG' or 'serialized DAG', > > SimpleDAG/SimpleTaskInstance used by scheduler are not needed > > 2. adding more fields to stringified DAGs to be compatible with > > scheduler > > > > 7. (long-term) Directly reading DAGs from DB in webserver > > 1. let webserver process fetch data from DB, instead of making a > DAG > > bag and refresh it > > 2. it solves the webserver inconsistency issue > > > > 8. (long-term) Event-driven DAG parsing > > 1. Instead of polling DAG files for updating/deleting DAGs, event > > based approaches, *e.g.*, inotify ( > > https://pypi.org/project/inotify_simple/) can be used > > > > > > > > > > > > On Mon, Jul 29, 2019 at 3:23 AM Kaxil Naik <kaxiln...@gmail.com> wrote: > > > > > Thanks all for the input and thanks Zhou too for the detailed AIP. > > > > > > The WIP PR can be a good first step to overall optimization. > > > > > > Let's sync-up on the progress you have already made & what we want to > > > target. > > > > > > @Jarek Potiuk <jarek.pot...@polidea.com> & @Fokko - If we manage to > > make > > > it entirely backward-compatible with an enable/disable flag as we > > > mentioned, we can think of including it in 1.10.5 but I am in favor of > > > removing / cleaning stuff like pickles, drop Py 2.0 and cut Airflow 2.0 > > and > > > include this change there. > > > > > > > > > > > > > > > On Mon, Jul 29, 2019 at 1:03 PM Jarek Potiuk <jarek.pot...@polidea.com > > > > > wrote: > > > > > > > Actually I am also doing a lot of v1-10-test merges during the last > few > > > > months (probably several tens of them already). Rarely the conflicts > > are > > > > difficult to solve in fact. We have usually small, localised changes > > and > > > > until we go for full Black file re-formatting, we should be ok (and > the > > > > change from Zhou seems rather small and localised). > > > > > > > > J. > > > > > > > > On Mon, Jul 29, 2019 at 9:25 AM Driesprong, Fokko > <fo...@driesprong.frl > > > > > > > wrote: > > > > > > > > > I would be hesitant to merge it into 1.10.5. When I try to backport > > > > > anything into the 1.x branch, I get a whole bunch on merge > conflicts, > > > > even > > > > > on the trivial tickets. For me, the only one who can really comment > > on > > > > this > > > > > would be Ash, since he's doing the bulk of the conflict resolving. > > > Apart > > > > > from that, I'm really excited to make this happen! > > > > > > > > > > Cheers, Fokko > > > > > > > > > > > > > > > > > > > > Op zo 28 jul. 2019 om 20:23 schreef Jarek Potiuk < > > > > jarek.pot...@polidea.com > > > > > >: > > > > > > > > > > > Some thought I have after looking at the proposal from Zhou. > > > > > > > > > > > > I think this is one of the most important things feature-wise for > > > > > Airflow. > > > > > > It looks like we have several in-progress attempts to solve the > > > problem > > > > > and > > > > > > I guess we should agree common approach. > > > > > > > > > > > > I like very much the approach of Zhou (AIP-24). It does seem to > > > > minimise > > > > > > the changes needed in Airflow and it means that we with some > > > > > optimisations > > > > > > (caching mentioned by Fokko) - it can solve the major pain points > > > and I > > > > > > think relatively quick and is potentially portable to 1.10.5 if > we > > > have > > > > > it. > > > > > > > > > > > > I wonder how much it overlaps/differs from what Kaxil and Ash > ideas > > > > are. > > > > > If > > > > > > I read it correctly - it sounds like this idea will contain some > > more > > > > > > "fundamental" changes. Ones that are likely less > > > backwards-compatible, > > > > > and > > > > > > potentially taking longer time to implement and test. And likely > > > > solving > > > > > > some of the problems better or even solving other problems. Am I > > > right > > > > > with > > > > > > my assumptions? > > > > > > > > > > > > I think more information on this might be helpful so that we all > > know > > > > if > > > > > > those are two different AIPs, or whether they can be joined in > one > > > > > effort, > > > > > > and how they relate to AIP-18/AIP-19 (should those be deprecated > or > > > > > > independently implemented ?). Also - since 2.0.0 release is half > a > > > year > > > > > > ahead we should consider how it impact the roadmap. > > > > > > > > > > > > I can see three approaches here that we as community can follow > > > (maybe > > > > I > > > > > am > > > > > > missing some :) ): > > > > > > > > > > > > 1) focus our work on single "complete" solution that will take > > longer > > > > > time > > > > > > and targets 2.0.0. > > > > > > 2) work on two of them: one quick/fast - potentially portable to > > > > 1.10.5m > > > > > > one longer-term for 2.0.0. > > > > > > 3) decide that the simple solution we have from Zhou (maybe with > > some > > > > > > modifications) is our target solution (for both 1.10.5 if we have > > it > > > > and > > > > > > 2.0.0): > > > > > > > > > > > > J. > > > > > > > > > > > > On Sat, Jul 27, 2019 at 11:43 AM Kevin Yang <yrql...@gmail.com> > > > wrote: > > > > > > > > > > > > > Nice job Zhou! > > > > > > > > > > > > > > Really excited, exactly what we wanted for the webserver > scaling > > > > issue. > > > > > > > Want to add another big drive for Airbnb to start think about > > this > > > > > > > previously to support the effort: it can not only bring > > consistency > > > > > > between > > > > > > > webservers but also bring consistency between webserver and > > > > > > > scheduler/workers. It may be less of a problem if total DAG > > parsing > > > > > time > > > > > > is > > > > > > > small, but for us the total DAG parsing time is 15+ mins and we > > had > > > > to > > > > > > set > > > > > > > the webserver( gunicorn subprocesses) restart interval to 20 > > mins, > > > > > which > > > > > > > leads to a worst case 15+20+15=50 mins delay between scheduler > > > start > > > > to > > > > > > > schedule things and users can see their deployed > DAGs/changes... > > > > > > > > > > > > > > I'm not so sure about the scheduler performance improvement: > > > > currently > > > > > we > > > > > > > already feed the main scheduler process with SimpleDag through > > > > > > > DagFileProcessorManager running in a subprocess--in the future > we > > > > feed > > > > > it > > > > > > > with data from DB, which is likely slower( tho the diff should > > have > > > > > > > negligible impact to the scheduler performance). In fact if > we'd > > > keep > > > > > the > > > > > > > existing behavior, try schedule only fresh parsed DAGs, then we > > may > > > > > need > > > > > > to > > > > > > > deal with some consistency issue--dag processor and the > scheduler > > > > race > > > > > > for > > > > > > > updating the flag indicating if the DAG is newly parsed. No big > > > deal > > > > > > there > > > > > > > but just some thoughts on the top of my head and hopefully can > be > > > > > > helpful. > > > > > > > > > > > > > > And good idea on pre-rendering the template, believe template > > > > rendering > > > > > > was > > > > > > > the biggest concern in the previous discussion. We've also > chose > > > the > > > > > > > pre-rendering+JSON approach in our smart sensor API > > > > > > > < > > > > > > > > > > > > > > > > > > > > > > > > > > > > https://cwiki.apache.org/confluence/display/AIRFLOW/AIP-17+Airflow+sensor+optimization > > > > > > > > > > > > > > > and > > > > > > > seems to be working fine--a supporting case for ur proposal ;) > > > > There's > > > > > a > > > > > > > WIP > > > > > > > PR <https://github.com/apache/airflow/pull/5499> for it just > in > > > case > > > > > you > > > > > > > are interested--maybe we can even share some logics. > > > > > > > > > > > > > > Thumbs-up again for this and please don't heisitate to reach > out > > if > > > > you > > > > > > > want to discuss further with us or need any help from us. > > > > > > > > > > > > > > > > > > > > > Cheers, > > > > > > > Kevin Y > > > > > > > > > > > > > > On Sat, Jul 27, 2019 at 12:54 AM Driesprong, Fokko > > > > > <fo...@driesprong.frl > > > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > Looks great Zhou, > > > > > > > > > > > > > > > > I have one thing that pops in my mind while reading the AIP; > > > should > > > > > > keep > > > > > > > > the caching on the webserver level. As the famous quote goes: > > > > *"There > > > > > > are > > > > > > > > only two hard things in Computer Science: cache invalidation > > and > > > > > naming > > > > > > > > things." -- Phil Karlton* > > > > > > > > > > > > > > > > Right now, the fundamental change that is being proposed in > the > > > AIP > > > > > is > > > > > > > > fetching the DAGs from the database in a serialized format, > and > > > not > > > > > > > parsing > > > > > > > > the Python files all the time. This will give already a great > > > > > > performance > > > > > > > > improvement on the webserver side because it removes a lot of > > the > > > > > > > > processing. However, since we're still fetching the DAGs from > > the > > > > > > > database > > > > > > > > in a regular interval, cache it in the local process, so we > > still > > > > > have > > > > > > > the > > > > > > > > two issues that Airflow is suffering from right now: > > > > > > > > > > > > > > > > 1. No snappy UI because it is still polling the database > in > > a > > > > > > regular > > > > > > > > interval. > > > > > > > > 2. Inconsistency between webservers because they might > poll > > > in a > > > > > > > > different interval, I think we've all seen this: > > > > > > > > https://www.youtube.com/watch?v=sNrBruPS3r4 > > > > > > > > > > > > > > > > As I also mentioned in the Slack channel, I strongly feel > that > > we > > > > > > should > > > > > > > be > > > > > > > > able to render most views from the tables in the database, so > > > > without > > > > > > > > touching the blob. For specific views, we could just pull the > > > blob > > > > > from > > > > > > > the > > > > > > > > database. In this case we always have the latest version, and > > we > > > > > tackle > > > > > > > the > > > > > > > > second point above. > > > > > > > > > > > > > > > > To tackle the first one, I also have an idea. We should > change > > > the > > > > > DAG > > > > > > > > parser from a loop to something that uses inotify > > > > > > > > https://pypi.org/project/inotify_simple/. This will change > it > > > from > > > > > > > polling > > > > > > > > to an event-driven design, which is much more performant and > > less > > > > > > > resource > > > > > > > > hungry. But this would be an AIP on its own. > > > > > > > > > > > > > > > > Again, great design and a comprehensive AIP, but I would > > include > > > > the > > > > > > > > caching on the webserver to greatly improve the user > experience > > > in > > > > > the > > > > > > > UI. > > > > > > > > Looking forward to the opinion of others on this. > > > > > > > > > > > > > > > > Cheers, Fokko > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Op za 27 jul. 2019 om 01:44 schreef Zhou Fang > > > > > > > <zhouf...@google.com.invalid > > > > > > > > >: > > > > > > > > > > > > > > > > > Hi Kaxi, > > > > > > > > > > > > > > > > > > Just sent out the AIP: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > https://cwiki.apache.org/confluence/display/AIRFLOW/AIP-24+DAG+Persistence+in+DB+using+JSON+for+Airflow+Webserver+and+%28optional%29+Scheduler > > > > > > > > > > > > > > > > > > Thanks! > > > > > > > > > Zhou > > > > > > > > > > > > > > > > > > > > > > > > > > > On Fri, Jul 26, 2019 at 1:33 PM Zhou Fang < > > zhouf...@google.com > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > Hi Kaxil, > > > > > > > > > > > > > > > > > > > > We are also working on persisting DAGs into DB using JSON > > for > > > > > > Airflow > > > > > > > > > > webserver in Google Composer. We target at minimizing the > > > > change > > > > > to > > > > > > > the > > > > > > > > > > current Airflow code. Happy to get synced on this! > > > > > > > > > > > > > > > > > > > > Here is our progress: > > > > > > > > > > (1) Serializing DAGs using Pickle to be used in webserver > > > > > > > > > > It has been launched in Composer. I am working on the PR > to > > > > > > upstream > > > > > > > > it: > > > > > > > > > > https://github.com/apache/airflow/pull/5594 > > > > > > > > > > Currently it does not support non-Airflow operators and > we > > > are > > > > > > > working > > > > > > > > on > > > > > > > > > > a fix. > > > > > > > > > > > > > > > > > > > > (2) Caching Pickled DAGs in DB to be used by webserver > > > > > > > > > > We have a proof-of-concept implementation, working on an > > AIP > > > > now. > > > > > > > > > > > > > > > > > > > > (3) Using JSON instead of Pickle in (1) and (2) > > > > > > > > > > Decided to use JSON because Pickle is not secure and > human > > > > > > readable. > > > > > > > > The > > > > > > > > > > serialization approach is very similar to (1). > > > > > > > > > > > > > > > > > > > > I will update the RP ( > > > > > https://github.com/apache/airflow/pull/5594) > > > > > > > to > > > > > > > > > > replace Pickle by JSON, and send our design of (2) as an > > AIP > > > > next > > > > > > > week. > > > > > > > > > > Glad to check together whether our implementation makes > > sense > > > > and > > > > > > do > > > > > > > > > > improvements on that. > > > > > > > > > > > > > > > > > > > > Thanks! > > > > > > > > > > Zhou > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Fri, Jul 26, 2019 at 7:37 AM Kaxil Naik < > > > > kaxiln...@gmail.com> > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > >> Hi all, > > > > > > > > > >> > > > > > > > > > >> We, at Astronomer, are going to spend time working on > DAG > > > > > > > > Serialisation. > > > > > > > > > >> There are 2 AIPs that are somewhat related to what we > plan > > > to > > > > > work > > > > > > > on: > > > > > > > > > >> > > > > > > > > > >> - AIP-18 Persist all information from DAG file in DB > > > > > > > > > >> < > > > > > > > > > >> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > https://cwiki.apache.org/confluence/display/AIRFLOW/AIP-18+Persist+all+information+from+DAG+file+in+DB > > > > > > > > > >> > > > > > > > > > > >> - AIP-19 Making the webserver stateless > > > > > > > > > >> < > > > > > > > > > >> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > https://cwiki.apache.org/confluence/display/AIRFLOW/AIP-19+Making+the+webserver+stateless > > > > > > > > > >> > > > > > > > > > > >> > > > > > > > > > >> We plan to use JSON as the Serialisation format and > store > > it > > > > as > > > > > a > > > > > > > blob > > > > > > > > > in > > > > > > > > > >> metadata DB. > > > > > > > > > >> > > > > > > > > > >> *Goals:* > > > > > > > > > >> > > > > > > > > > >> - Make Webserver Stateless > > > > > > > > > >> - Use the same version of the DAG across Webserver & > > > > > Scheduler > > > > > > > > > >> - Keep backward compatibility and have a flag > > (globally & > > > > at > > > > > > DAG > > > > > > > > > level) > > > > > > > > > >> to turn this feature on/off > > > > > > > > > >> - Enable DAG Versioning (extended Goal) > > > > > > > > > >> > > > > > > > > > >> > > > > > > > > > >> We will be preparing a proposal (AIP) after some > research > > > and > > > > > some > > > > > > > > > initial > > > > > > > > > >> work and open it for the suggestions of the community. > > > > > > > > > >> > > > > > > > > > >> We already had some good brain-storming sessions with > > > Twitter > > > > > > folks > > > > > > > > > (DanD > > > > > > > > > >> & > > > > > > > > > >> Sumit), folks from GoDataDriven (Fokko & Bas) & Alex > (from > > > > Uber) > > > > > > > which > > > > > > > > > >> will > > > > > > > > > >> be a good starting point for us. > > > > > > > > > >> > > > > > > > > > >> If anyone in the community is interested in it or has > some > > > > > > > experience > > > > > > > > > >> about > > > > > > > > > >> the same and want to collaborate please let me know and > > join > > > > > > > > > >> #dag-serialisation channel on Airflow Slack. > > > > > > > > > >> > > > > > > > > > >> Regards, > > > > > > > > > >> Kaxil > > > > > > > > > >> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > -- > > > > > > > > > > > > Jarek Potiuk > > > > > > Polidea <https://www.polidea.com/> | Principal Software Engineer > > > > > > > > > > > > M: +48 660 796 129 <+48660796129> > > > > > > [image: Polidea] <https://www.polidea.com/> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > -- > > > > > > > > Jarek Potiuk > > > > Polidea <https://www.polidea.com/> | Principal Software Engineer > > > > > > > > M: +48 660 796 129 <+48660796129> > > > > [image: Polidea] <https://www.polidea.com/> > > > > > > > > > > > > > -- > > > *Kaxil Naik* > > > *Big Data Consultant | DevOps Data Engineer* > > > *Certified *Google Cloud Data Engineer | *Certified* Apache Spark & > Neo4j > > > Developer > > > *LinkedIn*: https://www.linkedin.com/in/kaxil > > > > > >
