A Brief Tour of DataFu


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DataFu (now Apache DataFu) is a collection of user-defined functions for working with large-scale data in Hadoop and Pig. This library was born out of the need for a stable, well-tested library of UDFs for data mining and statistics. It is used at LinkedIn in many of our off-line workflows for data derived products like “People You May Know” and “Skills”. It contains functions for:

* PageRank
* Quantiles (median), variance, etc.
* Sessionization
* Convenience bag functions (e.g., set operations, enumerating bags, etc)
* Convenience utility functions (e.g., assertions, easier writing of EvalFuncs)
* and more…

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A Brief Tour of DataFu

  1. 1. A Brief Tour of DataFuMatthew HayesStaff Engineer, LinkedIn
  2. 2. About Me• @LinkedIn for 2+ years• Worked on skills & endorsements:– http://data.linkedin.com/projects/skills-and-expertise• Side projects:– http://data.linkedin.com/– http://data.linkedin.com/opensource/datafu– http://data.linkedin.com/opensource/white-elephant
  3. 3. History of DataFu• LinkedIn had lots of useful UDFs developed byseveral teams• Problems:– Not centralized, little code sharing– No automated tests• Solution:– Centralized library– Unit tests (PigUnit!)– Code coverage (Cobertura)• Open sourced September 2011
  4. 4. Examples
  5. 5. Session Statistics• Suppose we a have stream of user clicks.pv = LOAD pageviews.csv USING PigStorage(,)AS (memberId:int, time:long, url:chararray);• How to compute statistics on session length?– Median– Variance– Percentiles (90th, 95th)
  6. 6. Session Statistics• First, what is a session?• Session: sustained user activity• Lets assume session ends when 10 minutes elapsewith no activity.• Define the Sessionize UDF:DEFINE Sessionize datafu.pig.sessions.Sessionize(10m);DEFINE UnixToISO org.apache.pig.piggybank.evaluation.datetime.convert.UnixToISO();• Need to convert UNIX timestamp to ISO string:
  7. 7. Session Statistics• Define the statistics UDFs from DataFu:DEFINE Median datafu.pig.stats.StreamingMedian();DEFINE Quantiledatafu.pig.stats.StreamingQuantile(0.90,0.95);DEFINE VAR datafu.pig.stats.VAR();• Streaming implementations are approximate– Contributed by Josh Wills (Cloudera)• There are also non-streaming versions:– Require sorted input– Exact, but less efficient
  8. 8. Session Statistics• Time in this example is a long.• Sessionize needs an ISO string, so convert it:pv = FOREACH pvGENERATE UnixToISO(time) as isoTime,time,memberId;
  9. 9. Session Statistics• Sessionize each users click stream:pv_sessionized = FOREACH (GROUP pv BY memberId) {ordered = ORDER pv BY isoTime;GENERATE FLATTEN(Sessionize(ordered))AS (isoTime, time, memberId, sessionId);};pv_sessionized = FOREACH pv_sessionized GENERATEsessionId, memberId, time;• Session ID is appended to each tuple.• All tuples within same session have same ID.
  10. 10. Session Statistics• Compute session length in minutes:session_times =FOREACH (GROUP pv_sessionized BY (sessionId,memberId))GENERATE group.sessionId as sessionId,group.memberId as memberId,(MAX(pv_sessionized.time) -MIN(pv_sessionized.time))/ 1000.0 / 60.0 as session_length;
  11. 11. Session Statistics• Compute session length statistics:session_stats = FOREACH (GROUP session_times ALL) {GENERATEAVG(ordered.session_length) as avg_session,SQRT(VAR(ordered.session_length)) as std_dev_session,Median(ordered.session_length) as median_session,Quantile(ordered.session_length) as quantiles_session;};DUMP session_stats
  12. 12. Session Statistics• Which users had >95th percentile sessions?long_sessions =filter session_times bysession_length >session_stats.quantiles_session.quantile_0_95;very_engaged_users =DISTINCT (FOREACH long_sessions GENERATE memberId);DUMP very_engaged_users
  13. 13. Session Statistics• What if we want to count views per page peruser?pv_counts = FOREACH (GROUP pv BY (memberId,url)) GENERATEgroup.memberId as memberId,group.url as url,COUNT(pv) as cnt;• But refreshes and go-backs are not thatsignificant.• Multiple views across sessions are moremeaningful.
  14. 14. Session Statistics• Use TimeCount to sessionize the counts:define TimeCount datafu.pig.date.TimeCount(10m);pv_counts = FOREACH (GROUP pv BY (memberId,url)) {ordered = order pv by time;GENERATEgroup.memberId as memberId,group.url as url,TimeCount(ordered.(time)) as cnt;}• Uses the same principle as Sessionize UDF.
  15. 15. ASSERT• Filter function that blows up on 0.data = filter data by ASSERT((memberId >= 0 ? 1 : 0),member ID was negative, doh!);• Try it on 1,2,3,4,5,-1:– ERROR 2078: Caught error from UDF: datafu.pig.util.ASSERT[Assertion violated: member ID was negative, doh!]
  16. 16. WilsonBinConf• Computes confidence interval for a proportion• Assumes binomial distribution• For 99% confidence:define WilsonBinConfdatafu.pig.stats.WilsonBinConf(0.01);
  17. 17. WilsonBinConf• Example: Is a given coin fair?• Collect samples, compute interval forproportion.flips = LOAD flips.csv using PigStorage() as (result:int);flip_prop = foreach (GROUP flips ALL) generateSUM(flips.result) as success,COUNT(flips.result) as total;conf = FOREACH flip_prop GENERATEWilsonBinConf(success,total);
  18. 18. WilsonBinConf• 10 flips:– ((0.24815974093858853,0.8720694404004281))• 100 flips:– ((0.4518081551463118,0.6982365348191562))• 10,000 flips:– ((0.4986209024723033,0.524363847383827))• 100,000 flips:– ((0.4976073029016679,0.5057524741805967))
  19. 19. CountEach• Suppose we have a recommendation system, andweve tracked what items have been recommended.items = FOREACH items GENERATE memberId, itemId;• We want to produce a bag of items shown tousers with count for each item.• Output should look like:{memberId: int,items: {(itemId: long,cnt: long)}}
  20. 20. CountEach• Typically, we would first count (member,item)pairs:items = GROUP items BY (memberId,itemId);items = FOREACH items GENERATEgroup.memberId as memberId,group.itemId as itemId,COUNT(items) as cnt;
  21. 21. CountEach• Then we would group again on member:items = GROUP items BY memberId;items = FOREACH items generategroup as memberId,items.(itemId,cnt) as items;• But, this requires two MR jobs.
  22. 22. CountEach• Using CountEach, we can accomplish the samething with one MR job and less code:items = FOREACH (GROUP items BY memberId) generategroup as memerId,CountEach(items.(itemId)) as items;• Better performance too! In one test I ran:– Wall clock time: 50% reduction– Total task time: 33% reduction
  23. 23. AliasableEvalFunc• Pig has great support for UDFs• But, UDFs with many positional parametersare sometimes error prone.• Lets look at an example.
  24. 24. AliasableEvalFunc• Suppose we want to compute monthly paymentsfor various interest rates.mortgage = load mortgage.csv using PigStorage(|)as (principal:double,num_payments:int,interest_rates: bag {tuple(interest_rate:double)});
  25. 25. AliasableEvalFunc• Lets write a UDF to compute monthly payments.• Get the input parameters:@Overridepublic DataBag exec(Tuple input) throws IOException{Double principal = (Double)input.get(0);Integer numPayments = (Integer)input.get(1);DataBag interestRates = (DataBag)input.get(2);// ...
  26. 26. AliasableEvalFunc• Compute the monthly payment for each interest rate:DataBag output = BagFactory.getInstance().newDefaultBag();for (Tuple interestTuple : interestRates) {Double interest = (Double)interestTuple.get(0);double monthlyPayment =computeMonthlyPayment(principal,numPayments,interest);output.add(TupleFactory.getInstance().newTuple(monthlyPayment));}
  27. 27. AliasableEvalFunc• Apply the UDF:payments = FOREACH mortgage GENERATEMortgagePayment(principal,num_payments,interest_rates);• But, we have to remember the correct order.• This wont work:payments = FOREACH mortgage GENERATEMortgagePayment(num_payments,principal,interest_rates);
  28. 28. AliasableEvalFunc• AliasableEvalFunc to the rescue!• Get the parameters by name:Double principal = getDouble(input,"principal");Integer numPayments = getInteger(input,"num_payments");DataBag interestRates = getBag(input,"interest_rates");
  29. 29. AliasableEvalFunc• Get each interest rate from the bag:for (Tuple interestTuple : interestRates) {Double interest =getDouble(interestTuple,getPrefixedAliasName("interest_rates","interest_rate"));// compute monthly payment...}
  30. 30. AliasableEvalFunc• Now order doesnt matter, as long as namesare correct:payments = FOREACH mortgage GENERATEMortgagePayment(principal,num_payments,interest_rates);payments = FOREACH mortgage GENERATEMortgagePayment(num_payments,principal,interest_rates);
  31. 31. SetIntersect• Set intersection of two or more sorted bagsdefine SetIntersect datafu.pig.bags.sets.SetIntersect()-- input:-- ({(2),(3),(4)},{(1),(2),(4),(8)})input = FOREACH input {B1 = ORDER B1 BY val;B2 = ORDER B2 BY val;GENERATE SetIntersect(B1,B2);}-- ouput: ({(2),(4)})
  32. 32. SetUnion• Set union of two or more bagsdefine SetUnion datafu.pig.bags.sets.SetUnion();-- input:-- ({(2),(3),(4)},{(1),(2),(4),(8)})output = FOREACH input GENERATE SetUnion(B1,B2);-- output:-- ({(2),(3),(4),(1),(8)})
  33. 33. BagConcat• Concatenate tuples from set of bagsdefine BagConcat datafu.pig.bags.BagConcat();-- input:-- ({(1),(2),(3)},{(3),(4),(5)})output = FOREACH input GENERATE BagConcat(A,B);-- output:-- ({(1),(2),(3),(3),(4),(5)})
  34. 34. What Else Is There?• PageRank (in-memory implementation)• WeightedSample• NullToEmptyBag• AppendToBag• PrependToBag• ...
  35. 35. Thanks!• We welcome contributions:– https://github.com/linkedin/datafu
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