On Thu, Aug 22, 2013 at 3:45 PM, Micah Whitacre <[email protected]>wrote:
> I view them as separate pieces of functionality. The splitting of a > grouping PType (Pair, Tuple) seems reusable in a number of contexts. When > we support Unions (or Either) we could provide similar functionality to > split PCollection<Union<T, U>> -> Pair<PCollection<T>, PCollection<U>>. > That's a fair point. Okay, let's go ahead w/the PCollection<Pair<>> -> Pair<PCollection<>> plan. > > > On Thu, Aug 22, 2013 at 5:33 PM, Josh Wills <[email protected]> wrote: > >> I'm +1 for the PCollection<Pair<T, U>> -> Pair<PCollection<T>, >> PCollection<U>> approach outlined by Brandon and Chao. I think the only >> question is whether or not we want to add in the Union<T, U> (or Either<T, >> U>?) feature as part of doing that change. >> >> J >> >> >> On Wed, Aug 21, 2013 at 9:19 AM, Inman,Brandon >> <[email protected]>wrote: >> >>> This is close to how I had imagined the implementation to look. Very >>> roughly- >>> >>> public static class FirstEmittingDoFn<T extends Pair<U, ?>, U> extends >>> DoFn<Pair<U, ?>, U> { >>> >>> @Override >>> public void process(Pair<U, ?> input, Emitter<U> emitter) { >>> final U first = input.first(); >>> if (first != null) { >>> emitter.emit(first); >>> } >>> } >>> } >>> } >>> >>> There would be a very similar DoFn for second() that I'll omit for >>> brevity. I originally envisioned the utility method calling the DoFn that >>> generated the pair, but I like the idea of a smaller utility. The utility >>> method should be as simple as... >>> >>> public static <T, U> Pair<PCollection<T>,PCollection<U>> >>> filterChannels(final PCollection<Pair<T,U>> pCollection, final PType<T> >>> firstPType, final PType<U> secondPType) { >>> >>> final PCollection<T> stdout = collection.parallelDo(new >>> FirstEmittingDoFn<T>, firstPType); >>> final PCollection<U> stderr = collection.parallelDo(new >>> SecondEmittingDoFn<U>, secondPType); >>> >>> >>> return Pair.of(stdout,stderr); >>> } >>> >>> >>> Disclaimer; I didn't try to compile (all) this code, so treat as >>> pseudocode. >>> >>> From: Josh Wills <[email protected]> >>> Reply-To: "[email protected]" <[email protected]> >>> Date: Tuesday, August 20, 2013 9:40 PM >>> To: "[email protected]" <[email protected]> >>> Subject: Re: Multiple output channels from Crunch DoFn >>> >>> >>> That does sound pretty clean... >>> >>> >>> On Tue, Aug 20, 2013 at 7:34 PM, Chao Shi >>> <[email protected]> wrote: >>> >>> Is it possible to provide a utility that transforms PCollection<Pair<A, >>> B>> to Pair<PCollection<A>, PCollection<B>>? So one can simply emit Pairs >>> and then write them to two Targets. This could be generalized to Tuples. >>> >>> >>> 2013/8/21 Josh Wills <[email protected]> >>> >>> >>> On Tue, Aug 20, 2013 at 12:23 PM, Inman,Brandon < >>> [email protected]> >>> wrote: >>> >>> I like the flexibility of this approach, although would the idea of >>> having >>> some official constants defined for a small set of standard channels be >>> reasonable (the concepts of "out" and "error" are pretty common, others >>> may be warranted as well)? >>> >>> >>> >>> >>> >>> >>> So I think the way I would handle this would be having a main output >>> directory and an error output directory that was underneath it. Cascading >>> does this trick within their existing flows where you can throw >>> exceptions >>> to "traps," which is essentially the >>> same idea, though I'm not wild about control flow that relies on >>> throwing >>> exceptions. >>> >>> >>> >>> Is this something that you would see being added to core Crunch APIs (for >>> example, directly to Pipeline), or implemented on top of Crunch with a >>> filtering approach similar to my original post? If it's implemented on >>> top, shouldn't materialization work >>> as-is? >>> >>> >>> >>> >>> >>> >>> Yes, your model would be simpler. I think that mine would require a >>> special kind of Target implementation, a custom implementation of the >>> Emitter interface that would be used for routing the outputs of the DoFn, >>> and possibly some post-processing code to >>> move the data to a sensible place. I don't know if that work is strictly >>> necessary, and your impl is certainly much more straightforward than >>> mine. >>> :) >>> >>> >>> >>> >>> If the type was PTable<String, T>, could Union<S,U> be a choice for T as >>> appropriate? In our case, we would likely be looking at a PTable<String, >>> T >>> extends SpecificRecordBase> and not necessarily need Union with this >>> approach. >>> >>> >>> >>> >>> >>> >>> Yeah, I think it would be fine, but we'd have to be cognizant of it when >>> we were implementing the union type, and it would be up to the client to >>> ensure that the right data type ended up in the right file, which is >>> maybe >>> less good? >>> >>> >>> >>> >>> >>> From: Josh Wills <[email protected]> >>> Reply-To: "[email protected]" <[email protected]> >>> Date: Tuesday, August 20, 2013 1:00 PM >>> To: "[email protected]" <[email protected]> >>> Subject: Re: Multiple output channels from Crunch DoFn >>> >>> >>> A related idea that has come up a few times has been the idea of having a >>> way of writing values to different files based on a key: some kind of >>> generalization of Target that would itself write multiple outputs under >>> the covers, with the name >>> of the output file indicated by some function of the key of the PTable. >>> >>> For this situation, we would have a PTable that was like PTable<String, >>> Union<S, T>>, or just PTable<String, T> if the output types were all the >>> same, and the String would specify the name of an output directory (that >>> I >>> suppose would live underneath some base >>> output directory for the Target) that the record would be written to. >>> >>> There are a couple of limitations to this approach, I think: we couldn't >>> consider this kind of PTable "materialized" w/o doing an overhaul of the >>> materialization logic-- it would act sort of like an HTableTarget in that >>> it would be write-only in flows. >>> There are probably some others I can't think of off the top of my head. >>> What do you guys think? >>> >>> J >>> >>> >>> >>> On Tue, Aug 20, 2013 at 9:49 AM, Brush,Ryan >>> <[email protected]> wrote: >>> >>> I happen to have some context around this, so I wanted to expand on >>> Brandon's question a bit. The use case here is we're dealing with a >>> large >>> volume of third-party input and expect a certain percentage of bogus or >>> malformed data. Rather than simply logging >>> instances of bad records, we want to treat it as a signal we can learn >>> from, both for improving our processing logic and for creating structured >>> reports we can use to troubleshoot data sources. >>> >>> This leads to the "standard out" and "standard error" metaphors Brandon >>> mentions: in most cases, our Crunch DoFns would emit a processed >>> structure >>> useful downstream. But we'd also like to be able to emit a structured >>> error -- probably as an Avro object in our >>> case -- and persist that as a byproduct of our main processing pipeline. >>> >>> Would it make sense for such DoFn's to emit something some form of >>> "Option" object? We could then attach two consuming functions to it: one >>> that handles the "success" case, sending the resulting Avro object >>> downstream. Another DoFn attached to the "Option" >>> object would be a no-op unless the Option contained an "error" >>> structure, >>> at which point we persist it to some well-known location for later >>> analysis. >>> >>> I think this is entirely achievable using existing mechanisms...but it >>> seems like common enough use case (at least for us) to establish some >>> idioms for dealing it. >>> >>> On Aug 20, 2013, at 11:13 AM, Inman,Brandon wrote: >>> >>> > >>> > We've been looking at ways to do multiple outputs in Crunch jobs, >>> > specifically writing out some kind of Status or Error Avro object, >>> based >>> > on failures that occur processing individual records in various jobs. >>> It >>> > had been suggested that, rather than logging these errors to >>> traditional >>> > loggers, to consider them an output of the Crunch job. After some >>> > internal discussion, it was suggested to run the ideas past the Crunch >>> > community. >>> > >>> > >>> > A major goal we have is to end with all the error output in a location >>> > that makes it easy to run Hive queries or perform other MapReduce-style >>> > analysis to quickly view all errors across the larger system without >>> the >>> > need go to multiple facilities. This means standardizing on the Avro >>> > object, but it also necessitates decoupling the storage of the object >>> >from >>> > the "standard output" of the job. >>> > >>> > >>> > As Crunch DoFns support a single Emitter per invocation of process(), >>> the >>> > solution that gathered the most support would be to emit an object >>> >similar >>> > to Pair<>, where first would be the "standard out" and second would be >>> >the >>> > "standard error". A DoFn would generally only populate one (nothing >>> > preventing it from populating both if appropriate, but not really >>> >intended >>> > as a part of general use), and separate DoFns would filter out the two >>> > components of the pair and write the values to the appropriate targets. >>> > >>> > As far as the emitted pairing object; the concept of a tagged union was >>> > suggested although there currently isn't support in Java or Avro for >>> the >>> > concept; it was noted that >>> > >>> https://issues.apache.org/jira/browse/CRUNCH-239 >>> < >>> https://urldefense.proofpoint.com/v1/url?u=https://issues.apache.org/jira/ >>> >>> browse/CRUNCH-239&k=PmKqfXspAHNo6iYJ48Q45A%3D%3D%0A&r=RiPWMqlVaSiSs74U1fVjr >>> >>> SpZO%2FvyTEWUW1RhCH7Ftlg%3D%0A&m=ZOuvUFJf2XiQL4mXsKMy9ArJwoDf7VP6eNKgaIHMaf >>> >>> c%3D%0A&s=dceef88f8fadf4d34b61b47e1728bc63dda36ad51151ccfceb5c84ea45be0e82<https://urldefense.proofpoint.com/v1/url?u=https://issues.apache.org/jira/browse/CRUNCH-239&k=PmKqfXspAHNo6iYJ48Q45A%3D%3D%0A&r=RiPWMqlVaSiSs74U1fVjrSpZO%2FvyTEWUW1RhCH7Ftlg%3D%0A&m=ZOuvUFJf2XiQL4mXsKMy9ArJwoDf7VP6eNKgaIHMafc%3D%0A&s=dceef88f8fadf4d34b61b47e1728bc63dda36ad51151ccfceb5c84ea45be0e82> >>> > >>> might be a close >>> > candidate. Pair<> would meet the requirements, although it was >>> suggested >>> > that a simple object dedicated to the task could make a cleaner >>> approach. >>> > >>> > Any general thoughts on this approach? Are there any other patterns >>> that >>> > might serve us better, or anything on the Crunch roadmap that might be >>> > more appropriate? >>> > >>> > >>> > Brandon Inman >>> > Software Architect >>> > www.cerner.com <http://www.cerner.com> >>> > >>> > >>> > CONFIDENTIALITY NOTICE This message and any included attachments are >>> >from Cerner Corporation and are intended only for the addressee. The >>> >information contained in this message is confidential and may constitute >>> >inside or non-public information under international, >>> federal, or state securities laws. Unauthorized forwarding, printing, >>> copying, distribution, or use of such information is strictly prohibited >>> and may be unlawful. If you are not the addressee, please promptly delete >>> this message and notify the sender of the >>> delivery error by e-mail or you may call Cerner's corporate offices in >>> Kansas City, Missouri, U.S.A at >>> >>> (+1) (816)221-1024 <tel:%28%2B1%29%20%28816%29221-1024>. >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> -- >>> Director of Data Science >>> Cloudera >>> < >>> https://urldefense.proofpoint.com/v1/url?u=http://www.cloudera.com&k=PmKqf >>> >>> XspAHNo6iYJ48Q45A%3D%3D%0A&r=RiPWMqlVaSiSs74U1fVjrSpZO%2FvyTEWUW1RhCH7Ftlg% >>> >>> 3D%0A&m=ZOuvUFJf2XiQL4mXsKMy9ArJwoDf7VP6eNKgaIHMafc%3D%0A&s=508adfd2097ef3f >>> 7c9738fe9f729f47d95ae1d6568dabe09697317fd6d53f9d1<https://urldefense.proofpoint.com/v1/url?u=http://www.cloudera.com&k=PmKqfXspAHNo6iYJ48Q45A%3D%3D%0A&r=RiPWMqlVaSiSs74U1fVjrSpZO%2FvyTEWUW1RhCH7Ftlg%3D%0A&m=ZOuvUFJf2XiQL4mXsKMy9ArJwoDf7VP6eNKgaIHMafc%3D%0A&s=508adfd2097ef3f7c9738fe9f729f47d95ae1d6568dabe09697317fd6d53f9d1> >>> > >>> Twitter: >>> @josh_wills >>> < >>> https://urldefense.proofpoint.com/v1/url?u=http://twitter.com/josh_wills&k >>> >>> =PmKqfXspAHNo6iYJ48Q45A%3D%3D%0A&r=RiPWMqlVaSiSs74U1fVjrSpZO%2FvyTEWUW1RhCH >>> >>> 7Ftlg%3D%0A&m=ZOuvUFJf2XiQL4mXsKMy9ArJwoDf7VP6eNKgaIHMafc%3D%0A&s=585b666e2 >>> 90f5104a6f13a0fcbc52f4fc6cd93365dc1d44d3e49ed09c2fe1996<https://urldefense.proofpoint.com/v1/url?u=http://twitter.com/josh_wills&k=PmKqfXspAHNo6iYJ48Q45A%3D%3D%0A&r=RiPWMqlVaSiSs74U1fVjrSpZO%2FvyTEWUW1RhCH7Ftlg%3D%0A&m=ZOuvUFJf2XiQL4mXsKMy9ArJwoDf7VP6eNKgaIHMafc%3D%0A&s=585b666e290f5104a6f13a0fcbc52f4fc6cd93365dc1d44d3e49ed09c2fe1996> >>> > >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> -- >>> Director of Data Science >>> Cloudera >>> < >>> https://urldefense.proofpoint.com/v1/url?u=http://www.cloudera.com&k=PmKqf >>> >>> XspAHNo6iYJ48Q45A%3D%3D%0A&r=RiPWMqlVaSiSs74U1fVjrSpZO%2FvyTEWUW1RhCH7Ftlg% >>> >>> 3D%0A&m=JjOKxAMa8Miu4X1FpLdnSvt5WCGlwK4xE7i92OmAex0%3D%0A&s=1095ecaa17ab1e4 >>> 31966b19fec39773cae0b9319fc310155b4ab636cabd4799a<https://urldefense.proofpoint.com/v1/url?u=http://www.cloudera.com&k=PmKqfXspAHNo6iYJ48Q45A%3D%3D%0A&r=RiPWMqlVaSiSs74U1fVjrSpZO%2FvyTEWUW1RhCH7Ftlg%3D%0A&m=JjOKxAMa8Miu4X1FpLdnSvt5WCGlwK4xE7i92OmAex0%3D%0A&s=1095ecaa17ab1e431966b19fec39773cae0b9319fc310155b4ab636cabd4799a> >>> > >>> Twitter: >>> @josh_wills >>> < >>> https://urldefense.proofpoint.com/v1/url?u=http://twitter.com/josh_wills&k >>> >>> =PmKqfXspAHNo6iYJ48Q45A%3D%3D%0A&r=RiPWMqlVaSiSs74U1fVjrSpZO%2FvyTEWUW1RhCH >>> >>> 7Ftlg%3D%0A&m=JjOKxAMa8Miu4X1FpLdnSvt5WCGlwK4xE7i92OmAex0%3D%0A&s=8b9feeae6 >>> 0caabb4edd6caff1fd188790717924e130b1d3533089bee9a85e9a6<https://urldefense.proofpoint.com/v1/url?u=http://twitter.com/josh_wills&k=PmKqfXspAHNo6iYJ48Q45A%3D%3D%0A&r=RiPWMqlVaSiSs74U1fVjrSpZO%2FvyTEWUW1RhCH7Ftlg%3D%0A&m=JjOKxAMa8Miu4X1FpLdnSvt5WCGlwK4xE7i92OmAex0%3D%0A&s=8b9feeae60caabb4edd6caff1fd188790717924e130b1d3533089bee9a85e9a6> >>> > >>> >>> >> >> >> -- >> Director of Data Science >> Cloudera <http://www.cloudera.com> >> Twitter: @josh_wills <http://twitter.com/josh_wills> >> > > -- Director of Data Science Cloudera <http://www.cloudera.com> Twitter: @josh_wills <http://twitter.com/josh_wills>
