Hadoop and Machine Learning

Machine Learning and HadoopPresent and FutureJosh Wills, Tom Pierce, and Jeff HammerbacherCloudera Data Science TeamDecember 17th, 2011

Agenda• Part 1: Industrial Machine Learning• Part 2: Machine Learning and Hadoop • State of the World • Where Things Are Headed• Part 3: Things Industry Needs From Academia Copyright 2011 Cloudera Inc. All rights reserved

Delta One: Model Evaluation• ML Systems Are One Piece of a Complex System• Well-defined objective functions are the exception • Multiple, often conflicting goals • Weights are fuzzy and shift with business priorities • Pareto optimization is the safest play• Predictive Accuracy Is Only Useful Up to a Point• Examples • Computational advertising • Friend recommendations on social networks Copyright 2011 Cloudera Inc. All rights reserved

Delta Two: Systems Precede Algorithms• Greenfield Projects Hardly Ever Happen • (and don’t usually launch)• Industrial Computational Infrastructure • General-purpose • Cheap • Shared• Constraints Drive Innovation • Vowpal Wabbit Hashing Trick • SETI @ Google Copyright 2011 Cloudera Inc. All rights reserved

Delta Three: Workflow• Optimize the Overall Process • Model fitting is a small piece of the overall flow time • Parallelize everything• Better Features > Better Models• Fast Model Deployment • Common Feature Extraction Logic • Servable Models• Validation as Sanity Checking • Deploy to a small subset of real data and evaluate Copyright 2011 Cloudera Inc. All rights reserved

Hadoop Platform: Substrate• Commodity servers • Open Compute• Open source operating system • Linux• Open source configuration management • Puppet • Chef• Coordination service • ZooKeeper Copyright 2011 Cloudera Inc. All rights reserved

Hadoop Platform: Storage• Distributed schema-less storage • HDFS • Ceph• Append-only storage formats and metadata • Avro • RCFile • HCatalog• Mutable key-value storage and metadata • HBase Copyright 2011 Cloudera Inc. All rights reserved

Computation: Plain Old MapReduce• Great for: • Data Preparation • Feature Engineering • Model Validation/Evaluation• Works For Certain Model Fitting Problems • Recommendation Systems • Decision Trees (PLANET; Gradient Boosted Decision Trees)• Not A Practical Option for Online Learning• Way More Detail from the KDD 2011 Talk Copyright 2011 Cloudera Inc. All rights reserved

Tools for Data Preparation/Feature Engineering• Languages/Environments • PigLatin • HiveQL • Need to deal with mismatch between offline/online feature generation• Java/Scala APIs • Crunch (Cloudera) • Scoobi (NICTA) • Cascading (Concurrent) • Jaql (IBM) Copyright 2011 Cloudera Inc. All rights reserved

Apache Mahout• The starting place for MapReduce-based machine learning algorithms • Not machine-learning-in-a-box • Custom tweaks/modifications are the rule• A disparate collection of algorithms for: • Recommendations • Clustering • Classification • Frequent Itemset Mining Copyright 2011 Cloudera Inc. All rights reserved

Apache Mahout (cont.)• Best Library: Taste Recommender • Oldest project, most widely-deployed in production • SVD implementation is particularly active• Good Libraries: Online SGD • Does not use MapReduce • Vowpal Rabbit + AllReduce is faster, has L-BFGS option• Roll Your Own Instead: Naïve Bayes• Challenges • “Secret sauce” effect • Delta between Mahout + the cutting edge in ML Copyright 2011 Cloudera Inc. All rights reserved

More Machine Learning Interfaces for Hadoop• Based on MapReduce • SystemML (IBM) • AllReduce (Vowpal Wabbit)• No MapReduce • Spark• R-Based Systems (Augment MapReduce with R) • Segue • RHIPE • RHadoop • Ricardo (IBM) Copyright 2011 Cloudera Inc. All rights reserved

MRv2 and YARN• Eliminates JobTracker bottleneck • Separate Resource Manager/Scheduler • Individual jobs have their own task masters• Moves MapReduce into user-land• Enables Hadoop clusters to run all sorts of jobs • MPI (Hamster; MAPREDUCE-2911) • Native BSP (Giraph) • Spark • AllReduce, GraphLab Copyright 2011 Cloudera Inc. All rights reserved

Machine Learning on Multivariate Time Series • 1e5 writes/sec • Positive events are relatively rare • Feature extraction challenge • May not be clear what the right time horizon is • Tight SLAs • Very high stakes Copyright 2011 Cloudera Inc. All rights reserved

An Academic Language For Feature Engineering• Feature extraction/selection is as important as model fitting • e.g., hierarchical feature representation, impact on training time and experiment design, feature cost modeling, etc.• Academic literature on this problem is sparse and dispersed across multiple fields • NIPS 2003 • HCI, NLP, Information Retrieval, etc.• We need a common language for talking about these problems across disciplines Copyright 2011 Cloudera Inc. All rights reserved

A Broader Ontology For Model Selection• Practical factors that enter into the “best” choice of model… • Data arrival rate • Data volume • Scoring latency • Model refresh time • Robustness/reliability• …in addition to the standard predictive power/simplicity tradeoffs Copyright 2011 Cloudera Inc. All rights reserved

Questions?Want A Job? @josh_wills

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Hadoop and Machine Learning

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