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Validating Big Data Pipelines - Big Data Spain 2018


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As big data jobs move from the proof-of-concept phase into powering real production services, we have to start considering what will happen when everything eventually goes wrong (such as recommending inappropriate products or other decisions taken on bad data). This talk will attempt to convince you that we will all eventually get aboard the failboat (especially with ~40% of respondents automatically deploying their Spark jobs results to production), and it’s important to automatically recognize when things have gone wrong so we can stop deployment before we have to update our resumes.

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Validating Big Data Pipelines - Big Data Spain 2018

  1. 1. Validating Big Data & ML Pipelines With Apache Spark & Beam And Avoiding the Awk Now mostly “works”* Melinda Seckington
  2. 2. Some links (slides & recordings will be at): CatLoversShow
  3. 3. Holden: ● My name is Holden Karau ● Prefered pronouns are she/her ● Developer Advocate at Google ● Apache Spark PMC, Beam contributor ● previously IBM, Alpine, Databricks, Google, Foursquare & Amazon ● co-author of Learning Spark & High Performance Spark ● Twitter: @holdenkarau ● Slide share ● Code review livestreams: / ● Spark Talk Videos ● Talk feedback (if you are so inclined):
  4. 4. What is going to be covered: ● A super brief look at property testing ● What validation is & why you should do it for your data pipelines ● How to make simple validation rules & our current limitations ● ML Validation - Guessing if our black box is “correct” ● Cute & scary pictures ○ I promise at least one cat Andrew
  5. 5. Who I think you wonderful humans are? ● Nice* people ● Like silly pictures ● Possibly Familiar with one of Scala, Java, or Python? ● Possibly Familiar with one of Spark, BEAM, or a similar system (but also ok if not) ● Want to make better software ○ (or models, or w/e) ● Or just want to make software good enough to not have to keep your resume up to date
  6. 6. So why should you test? ● Makes you a better person ● Avoid making your users angry ● Save $s ○ Having an ML job fail in hour 26 to restart everything can be expensive... ● Waiting for our jobs to fail is a pretty long dev cycle ● Honestly you’re probably not watching this unless you agree
  7. 7. So why should you validate? ● tl;dr - Your tests probably aren’t perfect ● You want to know when you're aboard the failboat ● Our code will most likely fail at some point ○ Sometimes data sources fail in new & exciting ways (see “Call me Maybe”) ○ That jerk on that other floor changed the meaning of a field :( ○ Our tests won’t catch all of the corner cases that the real world finds ● We should try and minimize the impact ○ Avoid making potentially embarrassing recommendations ○ Save having to be woken up at 3am to do a roll-back ○ Specifying a few simple invariants isn’t all that hard ○ Repeating Holden’s mistakes is still not fun
  8. 8. So why should you test & validate: Results from: Testing with Spark survey
  9. 9. So why should you test & validate - cont Results from: Testing with Spark survey
  10. 10. Why don’t we test? ● It’s hard ○ Faking data, setting up integration tests ● Our tests can get too slow ○ Packaging and building scala is already sad ● It takes a lot of time ○ and people always want everything done yesterday ○ or I just want to go home see my partner ○ Etc. ● Distributed systems is particularly hard
  11. 11. Why don’t we test? (continued)
  12. 12. Why don’t we validate? ● We already tested our code ○ Riiiight? ● What could go wrong? Also extra hard in distributed systems ● Distributed metrics are hard ● not much built in (not very consistent) ● not always deterministic ● Complicated production systems
  13. 13. What happens when we don’t ● Personal stories go here ○ I have no comment about where these stories are from This talk is being recorded so we’ll leave it at: ● Negatively impacted the brand in difficult to quantify ways with words with multiple meanings ● Breaking a feature that cost a few million dollars ● Almost recommended illegal content (caught by a lucky manual) ● Every search result was a coffee shop itsbruce
  14. 14. Cat photo from
  15. 15. Where do folks get the data for pipeline tests? ● Most people generate data by hand ● If you have production data you can sample you are lucky! ○ If possible you can try and save in the same format ● If our data is a bunch of Vectors or Doubles Spark’s got tools :) ● Coming up with good test data can take a long time ● Important to test different distributions, input files, empty partitions etc. Lori Rielly
  16. 16. Property generating libs: QuickCheck / ScalaCheck ● QuickCheck (haskell) generates tests data under a set of constraints ● Scala version is ScalaCheck - supported by the two unit testing libraries for Spark ● Sscheck (scala check for spark) ○ Awesome people*, supports generating DStreams too! ● spark-testing-base ○ Also Awesome people*, generates more pathological (e.g. empty partitions etc.) RDDs *I assume PROtara hunt
  17. 17. With spark-testing-base & a million entries test("map should not change number of elements") { implicit val generatorDrivenConfig = PropertyCheckConfig(minSize = 0, maxSize = 1000000) val property = forAll(RDDGenerator.genRDD[String](sc)){ rdd => importantBussinesLogicFunction(rdd).count() == rdd.count() } check(property) }
  18. 18. But that can get a bit slow for all of our tests ● Not all of your tests should need a cluster (or even a cluster simulator) ● If you are ok with not using lambdas everywhere you can factor out that logic and test with traditional tools ● Or if you want to keep those lambdas - or verify the transformations logic without the overhead of running a local distributed systems you can try a library like kontextfrei ○ Don’t rely on this alone (but can work well with something like scalacheck)
  19. 19. Lets focus on validation some more: *Can be used during integration tests to further validate integration results
  20. 20. So how do we validate our jobs? ● The idea is, at some point, you made software which worked. ● Maybe you manually tested and sampled your results ● Hopefully you did a lot of other checks too ● But we can’t do that every time, our pipelines are no longer write-once run-once they are often write-once, run forever, and debug-forever. Photo by: Paul Schadler
  21. 21. How many people have something like this? val data = ... val parsed = data.flatMap(x => try { Some(parse(x)) } catch { case _ => None // Whatever, it's JSON } } Lilithis
  22. 22. But we need some data... val data = ... data.cache() val validData = data.filter(isValid) val badData = data.filter(! isValid(_)) if validData.count() < badData.count() { // Ruh Roh! Special business error handling goes here } ... Pager photo by Vitachao CC-SA 3
  23. 23. Well that’s less fun :( ● Our optimizer can’t just magically chain everything together anymore ● My is fnur :( ● Now I’m blocking on a thing in the driver Sn.Ho
  24. 24. Counters* to the rescue**! ● Both BEAM & Spark have their it own counters ○ Per-stage bytes r/w, shuffle r/w, record r/w. execution time, etc. ○ In UI can also register a listener from spark validator project ● We can add counters for things we care about ○ invalid records, users with no recommendations, etc. ○ Accumulators have some challenges (see SPARK-12469 for progress) but are an interesting option ● We can _pretend_ we still have nice functional code *Counters are your friends, but the kind of friends who steal your lunch money ** In a similar way to how regular expressions can solve problems…. Miguel Olaya
  25. 25. So what does that look like? val parsed = data.flatMap(x => try { Some(parse(x)) happyCounter.add(1) } catch { case _ => sadCounter.add(1) None // What's it's JSON } } // Special business data logic (aka wordcount) // Much much later* business error logic goes here Pager photo by Vitachao CC-SA 3 Phoebe Baker
  26. 26. Ok but what about those *s ● Both BEAM & Spark have their it own counters ○ Per-stage bytes r/w, shuffle r/w, record r/w. execution time, etc. ○ In UI can also register a listener from spark validator project ● We can add counters for things we care about ○ invalid records, users with no recommendations, etc. ○ Accumulators have some challenges (see SPARK-12469 for progress) but are an interesting option ● We can _pretend_ we still have nice functional code Miguel Olaya
  27. 27. General Rules for making Validation rules ● According to a sad survey most people check execution time & record count ● spark-validator is still in early stages but interesting proof of concept ● Sometimes your rules will miss-fire and you’ll need to manually approve a job ● Remember those property tests? Could be Validation rules ● Historical data ● Domain specific solutions Photo by: Paul Schadler
  28. 28. Turning property tests to validation rules* ● Yes in theory they’re already “tested” but... ● Common function to check accumulator value between validation & tests ● The real-world is can be fuzzier Photo by: Paul Schadler
  29. 29. Input Schema Validation ● Handling the “wrong” type of cat ● Many many different approaches ○ filter/flatMap stages ○ Working in Scala/Java? .as[T] ○ Manually specify your schema after doing inference the first time :p ● Unless your working on mnist.csv there is a good chance your validation is going to be fuzzy (reject some records accept others) ● How do we know if we’ve rejected too much? Bradley Gordon
  30. 30. As a relative rule: val (ok, bad) = (sc.accumulator(0), sc.accumulator(0)) val records ={ x => if (isValid(x)) ok +=1 else bad += 1 // Actual parse logic here } // An action (e.g. count, save, etc.) if (bad.value > 0.1* ok.value) { throw Exception("bad data - do not use results") // Optional cleanup } // Mark as safe P.S: If you are interested in this check out spark-validator (still early stages). Found Animals Foundation Follow
  31. 31. Validating records read matches our expectations: val vc = new ValidationConf(tempPath, "1", true, List[ValidationRule]( new AbsoluteSparkCounterValidationRule("recordsRead", Some(3000000), Some(10000000))) ) val sqlCtx = new SQLContext(sc) val v = Validation(sc, sqlCtx, vc) //Business logic goes here assert(v.validate(5) === true) } Photo by Dvortygirl
  32. 32. Counters in BEAM: (1 of 2) private final Counter matchedWords = Metrics.counter(FilterTextFn.class, "matchedWords"); private final Counter unmatchedWords = Metrics.counter(FilterTextFn.class, "unmatchedWords"); // Your special business logic goes here (aka shell out to Fortan or Cobol) Luke Jones
  33. 33. Counters in BEAM: (2 of 2) Long matchedWordsValue = metrics.metrics().queryMetrics( new MetricsFilter.Builder() .addNameFilter("matchedWords")).counters().next().committed(); Long unmatchedWordsValue = metrics.metrics().queryMetrics( new MetricsFilter.Builder() .addNameFilter("unmatchedWords")).counters().next().committed(); assertThat("unmatchWords less than matched words", unmatchedWordsValue, lessThan(matchedWordsValue)); Luke Jones
  34. 34. TFDV: Magic* ● Counters, schema inference, anomaly detection, oh my! # Compute statistics over a new set of data new_stats = tfdv.generate_statistics_from_csv(NEW_DATA) # Compare how new data conforms to the schema anomalies = tfdv.validate_statistics(new_stats, schema) # Display anomalies inline tfdv.display_anomalies(anomalies) Details: validation-data-understanding-validation-and-monitoring-at- scale-d38e3952c2f0
  35. 35. % of data change ● Not just invalid records, if a field’s value changes everywhere it could still be “valid” but have a different meaning ○ Remember that example about almost recommending illegal content? ● Join and see number of rows different on each side ● Expensive operation, but if your data changes slowly / at a constant ish rate ○ Sometimes done as a separate parallel job ● Can also be used on output if applicable ○ You do have a table/file/as applicable to roll back to right?
  36. 36. Not just data changes: Software too ● Things change! Yay! Often for the better. ○ Especially with handling edge cases like NA fields ○ Don’t expect the results to change - side-by-side run + diff ● Have an ML model? ○ Welcome to new params - or old params with different default values. ○ We’ll talk more about that later ● Excellent PyData London talk about how this can impact ML models ○ Done with sklearn shows vast differences in CVE results only changing the model number Francesco
  37. 37. Onto ML (or Beyond ETL :p) ● Some of the same principals work (yay!) ○ Schemas, invalid records, etc. ● Some new things to check ○ CV performance, Feature normalization ranges ● Some things don’t really work ○ Output size probably isn’t that great a metric anymore ○ Eyeballing the results for override is a lot harder contraption
  38. 38. Traditional theory (Models) ● Human decides it's time to “update their models” ● Human goes through a model update run-book ● Human does other work while their “big-data” job runs ● Human deploys X% new models ● Looks at graphs ● Presses deploy Andrew
  39. 39. Traditional practice (Models) ● Human is cornered by stakeholders and forced to update models ● Spends a few hours trying to remember where the guide is ● Gives up and kind of wings it ● Comes back to a trained model ● Human deploys X% models ● Human reads reddit/hacker news/etc. ● Presses deploy Bruno Caimi
  40. 40. New possible practice (sometimes) ● Computer kicks off job (probably at an hour boundary because *shrug*) to update model ● Workflow tool notices new model is available ● Computer deploys X% models ● Software looks at monitoring graphs, uses statistical test to see if it’s bad ● Robot rolls it back & pager goes off ● Human Presses overrides and deploys anyways Henrique Pinto
  41. 41. Extra considerations for ML jobs: ● Harder to look at output size and say if its good ● We can look at the cross-validation performance ● Fixed test set performance ● Number of iterations / convergence rate ● Number of features selected / number of features changed in selection ● (If applicable) delta in model weights or tree size or ... Jennifer C.
  42. 42. Cross-validation because saving a test set is effort ● Trains on X% of the data and tests on Y% ○ Multiple times switching the samples ● has the tools for auto fitting using CB ○ If your going to use this for auto-tuning please please save a test set ○ Otherwise your models will look awesome and perform like a ford pinto (or whatever a crappy car is here. Maybe a renault reliant?) Jonathan Kotta
  43. 43. False sense of security: ● A/B test please even if CV says many many $s ● Rank based things can have training bias with previous orders ● Non-displayed options: unlikely to be chosen ● Sometimes can find previous formulaic corrections ● Sometimes we can “experimentally” determine ● Other times we just hope it’s better than nothing ● Try and make sure your ML isn’t evil or re-encoding human biases but stronger
  44. 44. The state of serving is generally a mess ● If it’s not ML models its can be better ○ Reports for everyone! ○ Or database updates for everyone! ● Big challenge: when something goes wrong - how do I fix it? ○ Something will go wrong eventually - do you have an old snap shot you can roll back to quickly? ● One project which aims to improve this for ML is KubeFlow ○ Goal is unifying training & serving experiences ○ Despite the name targeting more than just TensorFlow ○ Doesn’t work with Spark yet, but it’s on my TODO list.
  45. 45. Updating your model ● The real world changes ● Online learning (streaming) is super cool, but hard to version ○ Common kappa-like arch and then revert to checkpoint ○ Slowly degrading models, oh my! ● Iterative batches: automatically train on new data, deploy model, and A/B test ● But A/B testing isn’t enough -- bad data can result in wrong or even illegal results (ask me after a bud light lime) Jennifer C.
  46. 46. Some ending notes ● Your validation rules don’t have to be perfect ○ But they should be good enough they alert infrequently ● You should have a way for the human operator to override. ● Just like tests, try and make your validation rules specific and actionable ○ # of input rows changed is not a great message - table XYZ grew unexpectedly to Y% ● While you can use (some of) your tests as a basis for your rules, your rules need tests too ○ e.g. add junk records/pure noise and see if it rejects James Petts
  47. 47. Related talks & blog posts ● Testing Spark Best Practices (Spark Summit 2014) ● Every Day I’m Shuffling (Strata 2015) & slides ● Spark and Spark Streaming Unit Testing ● Making Spark Unit Testing With Spark Testing Base ● Testing strategy for Apache Spark jobs ● The BEAM programming guide Interested in OSS (especially Spark)? ● Check out my Twitch & Youtube for livestreams - & Becky Lai
  48. 48. Related packages ● spark-testing-base: ● sscheck: ● spark-validator: *Proof of concept, do not actually use* ● spark-perf - ● spark-integration-tests - ● scalacheck - Becky Lai
  49. 49. Learning Spark Fast Data Processing with Spark (Out of Date) Fast Data Processing with Spark (2nd edition) Advanced Analytics with Spark Spark in Action High Performance SparkLearning PySpark
  50. 50. High Performance Spark! Available today, not a lot on testing and almost nothing on validation, but that should not stop you from buying several copies (if you have an expense account). Cat’s love it! Amazon sells it: :D
  51. 51. Sign up for the mailing list @
  52. 52. And some upcoming talks: ● November ○ Big Data Spain again (tomorrow @ 16:10) ○ Scale By The Bay - San Francisco ● December ○ ScalaX - London ● January ○ Data Day Texas ● February ○ TBD ● March ○ Strata San Francisco
  53. 53. Cat wave photo by Quinn Dombrowski k thnx bye! (or questions…) If you want to fill out survey: I will use update results in & give the talk again the next time Spark adds a major feature. Give feedback on this presentation Have questions? - SL18 - Union Grand EF I’m sadly heading out to Spark Summit right after this but e-mail me:
  54. 54. And including spark-testing-base up to spark 2.3.1 sbt: "com.holdenkarau" %% "spark-testing-base" % "2.3.1_0.10.0" % "test" Maven: <dependency> <groupId>com.holdenkarau</groupId> <artifactId>spark-testing-base_2.11</artifactId> <version>${spark.version}_0.10.0</version> <scope>test</scope> </dependency> Vladimir Pustovit
  55. 55. Other options for generating data: ● mapPartitions + Random + custom code ● RandomRDDs in mllib ○ Uniform, Normal, Possion, Exponential, Gamma, logNormal & Vector versions ○ Different type: implement the RandomDataGenerator interface ● Random
  56. 56. RandomRDDs val zipRDD = RandomRDDs.exponentialRDD(sc, mean = 1000, size = rows).map(_.toInt.toString) val valuesRDD = RandomRDDs.normalVectorRDD(sc, numRows = rows, numCols = numCols).repartition(zipRDD.partitions.size) val keyRDD = sc.parallelize(, zipRDD.getNumPartitions) keyRDD.zipPartitions(zipRDD, valuesRDD){ (i1, i2, i3) => new Iterator[(Long, String, Vector)] { ...
  57. 57. Testing libraries: ● Spark unit testing ○ spark-testing-base - ○ sscheck - ● Simplified unit testing (“business logic only”) ○ kontextfrei - * ● Integration testing ○ spark-integration-tests (Spark internals) - ● Performance ○ spark-perf (also for Spark internals) - ● Spark job validation ○ spark-validator - * Photo by Mike Mozart *Early stage or work-in progress, or proof of concept
  58. 58. Let’s talk about local mode ● It’s way better than you would expect* ● It does its best to try and catch serialization errors ● It’s still not the same as running on a “real” cluster ● Especially since if we were just local mode, parallelize and collect might be fine Photo by: Bev Sykes
  59. 59. Options beyond local mode: ● Just point at your existing cluster (set master) ● Start one with your shell scripts & change the master ○ Really easy way to plug into existing integration testing ● spark-docker - hack in our own tests ● YarnMiniCluster ○ BaseYarnClusterSuite.scala ○ In Spark Testing Base extend SharedMiniCluster ■ Not recommended until after SPARK-10812 (e.g. 1.5.2+ or 1.6+) Photo by Richard Masoner
  60. 60. Integration testing - docker is awesome ● Spark-docker, kafka-docker, etc. ○ Not always super up to date sadly - if you are last stable release A-OK, if you build from master - sad pandas ● Or checkout JuJu Charms (from Canonical) - ○ Makes it easy to deploy a bunch of docker containers together & configured in a reasonable way.
  61. 61. Setting up integration on Yarn/Mesos ● So lucky! ● You can write your tests in the same way as before - just read from your test data sources ● Missing a data source? ○ Can you sample it or fake it using the techniques from before? ○ If so - do that and save the result to your integration enviroment ○ If not… well good luck ● Need streaming integration? ○ You will probably need a second Spark (or other) job to generate the test data
  62. 62. “Business logic” only test w/kontextfrei import com.danielwestheide.kontextfrei.DCollectionOps trait UsersByPopularityProperties[DColl[_]] extends BaseSpec[DColl] { import DCollectionOps.Imports._ property("Each user appears only once") { forAll { starredEvents: List[RepoStarred] => val result = logic.usersByPopularity(unit(starredEvents)).collect().toList result.distinct mustEqual result } } … (continued in example/src/test/scala/com/danielwestheide/kontextfrei/example/)
  63. 63. Generating Data with Spark import org.apache.spark.mllib.random.RandomRDDs ... RandomRDDs.exponentialRDD(sc, mean = 1000, size = rows) RandomRDDs.normalVectorRDD(sc, numRows = rows, numCols = numCols)