Hi Eugene May we talk together next week ? I like the proposal. I would just need some details for my understanding.
Thanks Regards JB On Aug 11, 2016, 19:46, at 19:46, Eugene Kirpichov <kirpic...@google.com.INVALID> wrote: >Hi JB, > >What are your thoughts on this? > >I'm also thinking of having a virtual meeting to explain more about >this >proposal if necessary, since I understand it is a lot to digest. > >How about: Monday Aug 15, 8am-9am Pacific time, over Hangouts? >(link: >https://staging.talkgadget.google.com/hangouts/_/google.com/splittabledofn >- >I confirmed that it can be joined without being logged into a Google >account) > >Who'd be interested in attending, and does this time/date work for >people? > >On Fri, Aug 5, 2016 at 10:48 AM Eugene Kirpichov <kirpic...@google.com> >wrote: > >> Hi JB, thanks for reading and for your comments! >> >> It sounds like you are concerned about continued support for existing >IO's >> people have developed, and about backward compatibility? >> >> We do not need to remove the Source API, and all existing >Source-based >> connectors will continue to work [though the document proposes at >some >> point to make Read.from(Source) to translate to a wrapper SDF under >the >> hood, to exercise the feature more and to make sure that it is >strictly >> more powerful - but this is an optional implementation detail]. >> >> Perhaps the document phrases this too strongly - "replacing the >Source >> API": a better phrasing would be "introducing a new API so powerful >and >> easy-to-use that hopefully people will choose it over the Source API >all >> the time, even though they don't have to" :) And we can discuss >whether or >> not to actually deprecate/remove the Source API at some point down >the >> road, once it becomes clear whether this is the case or not. >> >> To give more context: this proposal came out of discussions within >the SDK >> team over the past ~1.5 years, before the Beam project existed, on >how to >> make major improvements to the Source API; perhaps it will clarify >things >> if I give a history of the ideas discussed: >> - The first idea was to introduce a Read.from(PCollection<Source>) >> transform while keeping the Source API intact - this, given >appropriate >> implementation, would solve most of the scalability and composability >> issues of IO's. Then most connectors would look like : ParDo<A, >Source<B>> >> + Read.from(). >> - Then we figured that the Source class is an unnecessary >abstraction, as >> it simply holds data. What if we only had a Reader<S, B> class where >S is >> the source type and B the output type? Then connectors would be >something >> like: ParDo<A, S> + hypothetical Read.using(Reader<S, B>). >> - Then somebody remarked that some of the features of Source are >useful to >> ParDo's as well: e.g. ability to report progress when processing a >very >> heavy element, or ability to produce very large output in parallel. >> - The two previous bullets were already hinting that the Read.using() >> primitive might not be so special: it just takes S and produces B: >isn't >> that what a ParDo does, plus some source magic, minus the convenience >of >> c.output() vs. the start/advance() state machine? >> - At this point it became clear that we should explore unifying >sources >> and ParDo's, in particular: can we bring the magic of sources to >ParDo's >> but without the limitations and coding inconveniences? And this is >how >> SplittableDoFn was born: bringing source magic to a DoFn by providing >a >> RangeTracker. >> - Once the idea of "splittable DoFn's" was born, it became clear that >it >> is strictly more general than sources; at least, in the respect that >> sources have to produce output, while DoFn's don't: an SDF may very >well >> produce no output at all, and simply perform a side effect in a >> parallel/resumable way. >> - Then there were countless hours of discussions on unifying the >> bounded/unbounded cases, on the particulars of RangeTracker APIs >> reconciling parallelization and checkpointing, what the relation >between >> SDF and DF should be, etc. They culminated in the current proposal. >The >> proposal comes at a time when a couple of key ingredients are >(almost) >> ready: NewDoFn to make SDF look like a regular DoFn, and the >State/Timers >> proposal to enable unbounded work per element. >> >> To put it shortly: >> - Yes, we will support existing Source connectors, and will support >> writing new ones, possibly forever. There is no interference with >current >> users of Source. >> - The new API is an attempt to improve the Source API, taken to its >> logical limit where it turns out that users' goals can be >accomplished >> easier and more generically entirely within ParDo's. >> >> Let me know what you think, and thanks again! >> >> On Fri, Aug 5, 2016 at 2:39 AM Jean-Baptiste Onofré <j...@nanthrax.net> >> wrote: >> >>> Hi Eugene, >>> >>> Just a question: why is it in DoFn and note an improvement of Source >? >>> >>> If I understand correctly, it means that we will have to refactore >all >>> existing IO: basically, what you propose is to remove all Source to >>> replace with NewDoFn. >>> >>> I'm concern with this approach, especially in term of timing: >clearly, >>> the IO is the area where we have to move forward in Beam as it will >>> allow new users to start in their projects. >>> So, we started to bring new IOs: Kafka, JMS, Cassandra, MongoDB, >JDBC, >>> ... and some people started to learn the IO API (Bounded/Unbouded >>> source, etc). >>> >>> I think it would make more sense to enhance the IO API (Source) >instead >>> of introducing a NewDoFn. >>> >>> What are your thoughts for IO writer like me ? ;) >>> >>> Regards >>> JB >>> >>> On 08/04/2016 07:45 PM, Eugene Kirpichov wrote: >>> > Hello Beam community, >>> > >>> > We (myself, Daniel Mills and Robert Bradshaw) would like to >propose >>> > "Splittable DoFn" - a major generalization of DoFn, which allows >>> processing >>> > of a single element to be non-monolithic, i.e. checkpointable and >>> > parallelizable, as well as doing an unbounded amount of work per >>> element. >>> > >>> > This allows effectively replacing the current >Bounded/UnboundedSource >>> APIs >>> > with DoFn's that are much easier to code, more scalable and >composable >>> with >>> > the rest of the Beam programming model, and enables many use cases >that >>> > were previously difficult or impossible, as well as some >non-obvious new >>> > use cases. >>> > >>> > This proposal has been mentioned before in JIRA [BEAM-65] and some >Beam >>> > meetings, and now the whole thing is written up in a document: >>> > >>> > https://s.apache.org/splittable-do-fn >>> > >>> > Here are some things that become possible with Splittable DoFn: >>> > - Efficiently read a filepattern matching millions of files >>> > - Read a collection of files that are produced by an earlier step >in the >>> > pipeline (e.g. easily implement a connector to a storage system >that can >>> > export itself to files) >>> > - Implement a Kafka reader by composing a "list partitions" DoFn >with a >>> > DoFn that simply polls a consumer and outputs new records in a >while() >>> loop >>> > - Implement a log tailer by composing a DoFn that incrementally >returns >>> new >>> > files in a directory and a DoFn that tails a file >>> > - Implement a parallel "count friends in common" algorithm (matrix >>> > squaring) with good work balancing >>> > >>> > Here is the meaningful part of a hypothetical Kafka reader written >>> against >>> > this API: >>> > >>> > ProcessContinuation processElement( >>> > ProcessContext context, OffsetRangeTracker tracker) { >>> > try (KafkaConsumer<String, String> consumer = >>> > Kafka.subscribe(context.element().topic, >>> > context.element().partition)) { >>> > consumer.seek(tracker.start()); >>> > while (true) { >>> > ConsumerRecords<String, String> records = >>> consumer.poll(100ms); >>> > if (records == null) return done(); >>> > for (ConsumerRecord<String, String> record : records) { >>> > if (!tracker.tryClaim(record.offset())) { >>> > return >>> resume().withFutureOutputWatermark(record.timestamp()); >>> > } >>> > context.output(record); >>> > } >>> > } >>> > } >>> > } >>> > >>> > The document describes in detail the motivations behind this >feature, >>> the >>> > basic idea and API, open questions, and outlines an incremental >delivery >>> > plan. >>> > >>> > The proposed API builds on the reflection-based new DoFn >[new-do-fn] >>> and is >>> > loosely related to "State and Timers for DoFn" [beam-state]. >>> > >>> > Please take a look and comment! >>> > >>> > Thanks. >>> > >>> > [BEAM-65] https://issues.apache.org/jira/browse/BEAM-65 >>> > [new-do-fn] https://s.apache.org/a-new-do-fn >>> > [beam-state] https://s.apache.org/beam-state >>> > >>> >>> -- >>> Jean-Baptiste Onofré >>> jbono...@apache.org >>> http://blog.nanthrax.net >>> Talend - http://www.talend.com >>> >>
