Lucene/Solr Revolution 2015: Where Search Meets Machine Learning

Where Search Meets Machine Learning Diana Hu @sdianahu — Data Science Lead, Verizon

Joaquin Delgado @joaquind — Director of Engineering, Verizon

Disclaimer

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The content of this presentation are of the authors’ personal statements and does not officially represent their employer’s view in anyway. Included content is especially not intended to convey the views of OnCue or Verizon

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Index

1.  Introduction 2.  Search and Information Retrieval 3.  ML problems as Search-based Systems 4.  ML Meets Search!

Introduction

Scaling learning systems is hard!

•  Millions of users, items

•  Billions of features

•  Imbalanced Datasets

•  Complex Distributed Systems

•  Many algorithms have not been tested at “Internet Scale”

Typical approaches

•  Distributed systems – Fault tolerance, Throughput vs. latency

•  Parallelization Strategies – Hashing, trees

•  Processing – Map reduce variants, MPI, graph parallel

•  Databases – Key/Value Stores, NoSQL

Such a custom system requires TLC

Search and Information Retrieval

Search

Search is about finding specific things that are either known or assumed to exist, Discovery is about is about helping the user encounter what he/she didn’t even know exists.

•  Focused on Search: Search Engines, Database Systems •  Focused on Discovery: Recommender Systems, Advertising

Predicate Logic and Declarative Languages Rock!

Search stack

Matched Hits

Representation Function

Similarity Calculation

Matched Hits Documents


Input Query

Matched Hits Matched Hits Retrieved Documents

Online Processing

Offline Processing

(*)Relevance Feedback

Query Representation

Doc Representation Index

*Metadata Engineering

(*) Optional

Relevance: Vector Space Model

Search Engines: the big hammer

•  Search engines are largely used to solve non-IR search problems, because: •  Widely Available

•  Fast and Scalable

•  Integrates well with existing data stores

But… Are we using the right tool?

•  Search Engines were originally designed for IR. •  Complex non-IR search tasks sometimes require a two

phase approach

Phase1) Filter Phase 2) Rank

Finding commonalities

Relevance aka Ranking

RecSys

Discovery

IR Search

Advertising

ML problems as Search-based Systems

Machine Learning

Machine Learning in particular supervised learning refer to techniques used to learn how to classify or score previously unseen objects based on a training dataset

Inference and Generalization are the Key!

Supervised learning pipeline

Learning systems’ stack

Visualization / UI

Retrieval

Ranking

Query Generation and Contextual Pre-filtering

Model Building

Index Building

Data/Events Collections

Data Analytics

Contextual Post Filtering

OnlineOffline

Experimentation

Case study: Recommender Systems

•  Reduce information load by estimating relevance •  Ranking (aka Relevance) Approaches: •  Collaborative filtering•  Content Based•  Knowledge Based•  Hybrid

•  Beyond rating prediction and ranking •  Business filtering logic•  Low latency and Scale

RecSys: Content based models •  Rec Task: Given a user profile find the best matching items by their

attributes •  Similarity calculation: based on keyword overlap between user/items •  Neighborhood method (i.e. nearest neighbor)

•  Query-based retrieval (i.e Rocchio’s method)

•  Probabilistic methods (classical text classification)

•  Explicit decision models

•  Feature representation: based on content analysis •  Vector space model

•  TF-IDF

•  Topic Modeling

RecSys: Collaborative Filtering

Matrix Factorization

Rating Dataset

User Factors

Item Factors

Re-Ranking Model

Input Query

Online Processing

Offline Processing

Recommendations

RecSys: Collaborative Filtering

Matrix Factorization

Rating Dataset

User Factors

Item Factors

Re-Ranking Model

Input Query

Online Processing

Offline Processing

Recommendations

ML Meets Search! ML Search

Remember the elephant?

Visualization / UI

Retrieval

Ranking


Model Building

Index Building


Data Analytics

Contextual Post Filtering

OnlineOffline

Experimentation

Simplifying the stack!

Visualization / UI


Model Building

Index Building


Data Analytics

OnlineOffline

Experimentation

RetrievalContextual Post Filtering

Ranking

Search stack

Matched Hits





Input Query


Online Processing

Offline Processing





(*) Optional

Simplifying the Search stack

Matched Hits





Input Query


Online Processing

Offline Processing





(*) Optional

Retrieval Contextual Post Filtering

Ranking

ML-Scoring PluginSerialized ML Model

ML-Scoring architecture

Lucene/Solr

Instances + Labels

Instances Index

ML Scoring Plugin

Serialized ML Model

Online Processing

Offline Processing

Trainer +

Indexer

ML-Scoring Options •  Option A: Solr FunctionQuery •  Pro: Model is just a query!•  Cons: Limits expressiveness of models

•  Option B: Solr Custom Function Query •  Pro: Loading any type of model (also PMML)•  Cons: Memory limitations, also multiple model reloading

•  Option C: Lucene CustomScoreQuery •  Pro: Can use PMML and tune how PMML gets loaded•  Cons: No control on matches•  Option D: Lucene Low level Custome Query •  *Mahout vectors from Lucene text (only trains, so not an option)

Real-life Problem

•  Census database that contains documents with the following fields: 1. Age: continuous; 2. Workclass: 8 values; 3. Fnlwgt: continuous.; 4. Education: 16 values; 5. Education-num: continuous.; 6. Marital-status: 7 values; 7. Occupation: 14 values; 8. Relationship: 6 values; 9. Race: 5 values; 10. Sex: Male, Female; 11. Capital-gain: continuous.;12. Capital-loss: continuous.; 13. Hours-per-week: continuous.; 14. Native-country: 41 values; 15. >50K Income: Yes, No.

•  Task is to predict whether a person makes more than 50k a year based on their attributes

1) Learn from the (training) data

Naïve Bayes SVM

Logistic Regression

Decision Trees

Train with your favorite ML Framework

Option A: Just a Solr Function Query

q=“sum(C, product(age,w1), product(Workclass,w2), product(Fnlwgt, w3), product(Education, w4), ….)”

Serialized ML Model as Query

Trainer +

Indexer Y_prediction = C + XB

May result in a crazy Solr functionQuery

See more at https://wiki.apache.org/solr/FunctionQuery

q=dismax&bf="ord(educaton-num)^0.5 recip(rord(age),1,1000,1000)^0.3"

What about models like this?

Option B: Custom Solr FuntionQuery 1.  Subclass org.apache.solr.search.ValueSourceParser.

public class MyValueSourceParser extends ValueSourceParser { public void init (NamedList namedList) {

… }

public ValueSource parse(FunctionQParser fqp) throws ParseException { return new MyValueSource(); } }

2.  In solrconfig.xml, register your new ValueSourceParser directly under the <config> tag <valueSourceParser name=“myfunc” class=“com.custom.MyValueSourceParser” />

3.  Subclass org.apache.solr.search.ValueSource and instantiate it in ValueSourceParser.parse()

Option C: Lucene CustomScoreQuery

2C) Serialize model with PMML •  Can use JPMML library to read serialized model in Lucene

•  On Lucene will need to implement an extension with JPMML-evaluator to take vectors as expected

3C) In Lucene: •  Override CustomScoreQuery: load PMML

•  Create CustomScoreProvider: do model PMML data marshaling

•  Rescoring: PMML evaluation

Predictive Model Markup Language

•  Why use PMML •  Allows users to build a model in one system•  Export model and deploy it in a different environment for prediction•  Fast iteration: from research to deployment to production

•  Model is a XML document with: •  Header: description of model, and where it was generated

•  DataDictionary: defines fields used by model

•  Model: structure and parameters of model

•  http://dmg.org/pmml/v4-2-1/GeneralStructure.html

Example: Train in Spark to PMML import org.apache.spark.mllib.clustering.KMeans import org.apache.spark.mllib.linalg.Vectors // Load and parse the data val data = sc.textFile("/path/to/file") .map(s => Vectors.dense(s.split(',').map(_.toDouble))) // Cluster the data into three classes using KMeans val numIterations = 20 val numClusters = 3 val kmeansModel = KMeans.train(data, numClusters, numIterations) // Export clustering model to PMML kmeansModel.toPMML("/path/to/kmeans.xml")

PMML XML File

Overriding scores with CustomScoreQuery

CustomScoreProvider CustomScoreQuery

Lucene Query

Find next Match

Score

Rescore Doc

New Score

*Credit to Doug Turnbull’s Hacking Lucene forCustom Search Results

Overriding scores with CustomScoreQuery

•  Matching remains •  Scoring overridden

CustomScoreProvider CustomScoreQuery

Lucene Query

Find next Match

Score

Rescore Doc

New Score

*Credit to Doug Turnbull’s Hacking Lucene forCustom Search Results

Implementing CustomScoreQuery

1.  Given normal Lucene Query, use a CustomScoreQuery to wrap it TermQuery q = New TermQuery(term)

MyCustomScoreQuery mcsq = New MyCustomScoreQuery(q)

//Make sure query has all fields needed by PMML!


2.  Initialize PMML

PMML pmml = ...;

ModelEvaluatorFactory modelEvaluatorFactory = ModelEvaluatorFactory.newInstance();

ModelEvaluator<?> modelEvaluator = modelEvaluatorFactory.newModelManager(pmml);

Evaluator evaluator = (Evaluator)modelEvaluator;


2.  Rescore each doc with IndexReader and docID

public float customScore(int doc, float subQueryScore, float valSrcScores[]) throws IOException {

//Lucene reader IndexReader r = context.reader(); Terms tv = r.getTermVector(doc, _field); TermsEnum tenum = null; tenum = tv.iterator(tenum); //convert the iterator order to fields needed by model

TermsEnum tenumPMML = tenum2PMML(tenum, evaluator.getActiveFields());


2.  Rescore each doc with IndexReader and docID //Marshall Data into PMML

Map<FieldName, FieldValue> arguments = new LinkedHashMap<FieldName, FieldValue>(); List<FieldName> activeFields = evaluator.getActiveFields();

for(FieldName activeField : activeFields){ // The raw is value has been sorted with number of fields needed Object rawValue = tenumPMML.next; FieldValue activeValue = evaluator.prepare(activeField, rawValue); arguments.put(activeField, activeValue); }


2.  Rescore each doc with IndexReader and docID //Rescore and evaluate with PMML

Map<FieldName, ?> results = evaluator.evaluate(arguments);

FieldName targetName = evaluator.getTargetField();

Object targetValue = results.get(targetName);

return (float) targetValue;

Potential issues

•  Performance •  If search space is very large

•  If model complexity explodes (i.e. kernel expansion)

•  Operations •  Code is running on key infrastructure

•  Versioning

•  Binary Compatibility

Option D: Low Level Lucene •  CustomScoreQuery or Custom FunctionScore can’t control

matches •  If you want custom matches and scoring…. •  Implement:

•  Custom Query Class

•  Custom Weight Class

•  Custom Scorer Class

•  http://opensourceconnections.com/blog/2014/03/12/using-customscorequery-for-custom-solrlucene-scoring/

Conclusion

•  Importance of the full picture – Learning systems from the lenses of the whole elephant

•  Reducing the time from science to production is complicated

•  Scalability is hard! •  Why not have ML use Search in its core during online eval?

•  Solr and Lucene are a start to customize your learning system

We are Hiring!

Contact me at [email protected]

@sdianahu Q&A

O C T O B E R 1 3 - 1 6 , 2 0 1 6 • A U S T I N , T X

Data & Analytics

Lucene/Solr Revolution 2015: Where Search Meets Machine Learning