On Sun, Feb 18, 2018 at 10:25 AM Romain Manni-Bucau <rmannibu...@gmail.com> wrote:
> 2018-02-18 19:19 GMT+01:00 Eugene Kirpichov <kirpic...@google.com>: > >> FinishBundle has a stronger guarantee: if the pipeline succeeded, then it >> has been called for every succeeded bundle, and succeeded bundles together >> cover the entire input PCollection. Of course, it may not have been called >> for failed bundles. >> To anticipate a possible objection "why not also keep retrying Teardown >> until it succeeds" - because if Teardown wasn't called on a DoFn instance, >> it's because the instance no longer exists and there's nothing to call it >> on. >> >> Please take a look at implementations of WriteFiles and BigQueryIO.read() >> and write() to see how cleanup of heavyweight resources (large number of >> temp files, temporary BigQuery datasets) can be achieved reliably to the >> extent possible. >> > > Do you mean passing state accross the fn and having a fn responsible of > the cleanup? Kind of making the teardown a processelement? This is a nice > workaround but it is not always possible as mentionned. Ismael even has a > nice case where this just fails and teardown would work - was with AWS, not > a bigquery bug, but same design. > I don't remember this case and would appreciate being reminded what it is. But in general, yes, there unfortunately exist systems designed in a way that reliably achieving cleanup when interacting with them from a fault-tolerant distributed system like Beam is simply impossible. We should consider on a case-by-case basis whether any given system is like this, and what to do if it is. > > >> >> On Sun, Feb 18, 2018 at 9:56 AM Romain Manni-Bucau <rmannibu...@gmail.com> >> wrote: >> >>> 2018-02-18 18:36 GMT+01:00 Eugene Kirpichov <kirpic...@google.com>: >>> >>>> "Machine state" is overly low-level because many of the possible >>>> reasons can happen on a perfectly fine machine. >>>> If you'd like to rephrase it to "it will be called except in various >>>> situations where it's logically impossible or impractical to guarantee that >>>> it's called", that's fine. Or you can list some of the examples above. >>>> >>> >>> Sounds ok to me >>> >>> >>>> >>>> The main point for the user is, you *will* see non-preventable >>>> situations where it couldn't be called - it's not just intergalactic >>>> crashes - so if the logic is very important (e.g. cleaning up a large >>>> amount of temporary files, shutting down a large number of VMs you started >>>> etc), you have to express it using one of the other methods that have >>>> stricter guarantees (which obviously come at a cost, e.g. no >>>> pass-by-reference). >>>> >>> >>> FinishBundle has the exact same guarantee sadly so not which which other >>> method you speak about. Concretely if you make it really unreliable - this >>> is what best effort sounds to me - then users can use it to clean anything >>> but if you make it "can happen but it is unexpected and means something >>> happent" then it is fine to have a manual - or auto if fancy - recovery >>> procedure. This is where it makes all the difference and impacts the >>> developpers, ops (all users basically). >>> >>> >>>> >>>> On Sun, Feb 18, 2018 at 9:16 AM Romain Manni-Bucau < >>>> rmannibu...@gmail.com> wrote: >>>> >>>>> Agree Eugene except that "best effort" means that. It is also often >>>>> used to say "at will" and this is what triggered this thread. >>>>> >>>>> I'm fine using "except if the machine state prevents it" but "best >>>>> effort" is too open and can be very badly and wrongly perceived by users >>>>> (like I did). >>>>> >>>>> >>>>> Romain Manni-Bucau >>>>> @rmannibucau <https://twitter.com/rmannibucau> | Blog >>>>> <https://rmannibucau.metawerx.net/> | Old Blog >>>>> <http://rmannibucau.wordpress.com> | Github >>>>> <https://github.com/rmannibucau> | LinkedIn >>>>> <https://www.linkedin.com/in/rmannibucau> | Book >>>>> <https://www.packtpub.com/application-development/java-ee-8-high-performance> >>>>> >>>>> 2018-02-18 18:13 GMT+01:00 Eugene Kirpichov <kirpic...@google.com>: >>>>> >>>>>> It will not be called if it's impossible to call it: in the example >>>>>> situation you have (intergalactic crash), and in a number of more common >>>>>> cases: eg in case the worker container has crashed (eg user code in a >>>>>> different thread called a C library over JNI and it segfaulted), JVM bug, >>>>>> crash due to user code OOM, in case the worker has lost network >>>>>> connectivity (then it may be called but it won't be able to do anything >>>>>> useful), in case this is running on a preemptible VM and it was preempted >>>>>> by the underlying cluster manager without notice or if the worker was too >>>>>> busy with other stuff (eg calling other Teardown functions) until the >>>>>> preemption timeout elapsed, in case the underlying hardware simply failed >>>>>> (which happens quite often at scale), and in many other conditions. >>>>>> >>>>>> "Best effort" is the commonly used term to describe such behavior. >>>>>> Please feel free to file bugs for cases where you observed a runner not >>>>>> call Teardown in a situation where it was possible to call it but the >>>>>> runner made insufficient effort. >>>>>> >>>>>> On Sun, Feb 18, 2018, 9:02 AM Romain Manni-Bucau < >>>>>> rmannibu...@gmail.com> wrote: >>>>>> >>>>>>> 2018-02-18 18:00 GMT+01:00 Eugene Kirpichov <kirpic...@google.com>: >>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> On Sun, Feb 18, 2018, 2:06 AM Romain Manni-Bucau < >>>>>>>> rmannibu...@gmail.com> wrote: >>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> Le 18 févr. 2018 00:23, "Kenneth Knowles" <k...@google.com> a >>>>>>>>> écrit : >>>>>>>>> >>>>>>>>> On Sat, Feb 17, 2018 at 3:09 PM, Romain Manni-Bucau < >>>>>>>>> rmannibu...@gmail.com> wrote: >>>>>>>>>> >>>>>>>>>> If you give an example of a high-level need (e.g. "I'm trying to >>>>>>>>>> write an IO for system $x and it requires the following >>>>>>>>>> initialization and >>>>>>>>>> the following cleanup logic and the following processing in >>>>>>>>>> between") I'll >>>>>>>>>> be better able to help you. >>>>>>>>>> >>>>>>>>>> >>>>>>>>>> Take a simple example of a transform requiring a connection. >>>>>>>>>> Using bundles is a perf killer since size is not controlled. Using >>>>>>>>>> teardown >>>>>>>>>> doesnt allow you to release the connection since it is a best effort >>>>>>>>>> thing. >>>>>>>>>> Not releasing the connection makes you pay a lot - aws ;) - or >>>>>>>>>> prevents you >>>>>>>>>> to launch other processings - concurrent limit. >>>>>>>>>> >>>>>>>>> >>>>>>>>> For this example @Teardown is an exact fit. If things die so badly >>>>>>>>> that @Teardown is not called then nothing else can be called to close >>>>>>>>> the >>>>>>>>> connection either. What AWS service are you thinking of that stays >>>>>>>>> open for >>>>>>>>> a long time when everything at the other end has died? >>>>>>>>> >>>>>>>>> >>>>>>>>> You assume connections are kind of stateless but some >>>>>>>>> (proprietary) protocols requires some closing exchanges which are not >>>>>>>>> only >>>>>>>>> "im leaving". >>>>>>>>> >>>>>>>>> For aws i was thinking about starting some services - machines - >>>>>>>>> on the fly in a pipeline startup and closing them at the end. If >>>>>>>>> teardown >>>>>>>>> is not called you leak machines and money. You can say it can be done >>>>>>>>> another way...as the full pipeline ;). >>>>>>>>> >>>>>>>>> I dont want to be picky but if beam cant handle its components >>>>>>>>> lifecycle it can be used at scale for generic pipelines and if bound >>>>>>>>> to >>>>>>>>> some particular IO. >>>>>>>>> >>>>>>>>> What does prevent to enforce teardown - ignoring the interstellar >>>>>>>>> crash case which cant be handled by any human system? Nothing >>>>>>>>> technically. >>>>>>>>> Why do you push to not handle it? Is it due to some legacy code on >>>>>>>>> dataflow >>>>>>>>> or something else? >>>>>>>>> >>>>>>>> Teardown *is* already documented and implemented this way >>>>>>>> (best-effort). So I'm not sure what kind of change you're asking for. >>>>>>>> >>>>>>> >>>>>>> Remove "best effort" from the javadoc. If it is not call then it is >>>>>>> a bug and we are done :). >>>>>>> >>>>>>> >>>>>>>> >>>>>>>> >>>>>>>>> Also what does it mean for the users? Direct runner does it so if >>>>>>>>> a user udes the RI in test, he will get a different behavior in prod? >>>>>>>>> Also >>>>>>>>> dont forget the user doesnt know what the IOs he composes use so this >>>>>>>>> is so >>>>>>>>> impacting for the whole product than he must be handled IMHO. >>>>>>>>> >>>>>>>>> I understand the portability culture is new in big data world but >>>>>>>>> it is not a reason to ignore what people did for years and do it wrong >>>>>>>>> before doing right ;). >>>>>>>>> >>>>>>>>> My proposal is to list what can prevent to guarantee - in the >>>>>>>>> normal IT conditions - the execution of teardown. Then we see if we >>>>>>>>> can >>>>>>>>> handle it and only if there is a technical reason we cant we make it >>>>>>>>> experimental/unsupported in the api. I know spark and flink can, any >>>>>>>>> unknown blocker for other runners? >>>>>>>>> >>>>>>>>> Technical note: even a kill should go through java shutdown hooks >>>>>>>>> otherwise your environment (beam enclosing software) is fully >>>>>>>>> unhandled and >>>>>>>>> your overall system is uncontrolled. Only case where it is not true >>>>>>>>> is when >>>>>>>>> the software is always owned by a vendor and never installed on >>>>>>>>> customer >>>>>>>>> environment. In this case it belongd to the vendor to handle beam API >>>>>>>>> and >>>>>>>>> not to beam to adjust its API for a vendor - otherwise all unsupported >>>>>>>>> features by one runner should be made optional right? >>>>>>>>> >>>>>>>>> All state is not about network, even in distributed systems so >>>>>>>>> this is key to have an explicit and defined lifecycle. >>>>>>>>> >>>>>>>>> >>>>>>>>> Kenn >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>
