Building a smart recommender system across LINE services

Jun Namikawa
LINE Machine Learning Team Fellow
https://linedevday.linecorp.com/jp/2019/sessions/C1-7

Transcript

1. 2019 DevDay Building a Smart Recommender System Across LINE Services > Jun Namikawa > LINE Machine Learning Team Fellow
2. Introduction
3. LINE Services
4. > Display recommended content and advertisements at the top of the chat tab Smart Channel
6. Overview Concept of Smart Channel Feed Contents Personalize
7. History of Smart Channel Country: JP
8. History of Smart Channel Country: JP
9. > Day2: C2-1 12:00-12:40 "LINE-Like" Product Management > Poster Session 13:40-14:20/15:30-16:10 (2days) > Day1: B1-2 14:30-15:10 The Art of Smart Channel Continuous Improvements in Smart Channel Platform/Contents Related Sections
10. ML Architecture
11. Recommender System for Smart Channel Constraints Cooperation with existing recommender systems Cold start problem Scalability
12. Many Recommender Systems Exist in LINE Each system has a different > Implementation > Algorithm > Objective
13. Smart Channel 2019-10 (Global) Current Stats Impressions / Day 500M Contents / Day 60K+ Global DAU 100M+
14. Only New Content Has Value
15. Recommender System Architecture Recommende r System 
 for Service Recommender System 
 for Service Recommender System 
 for Service Recommender System 
 for Service Recommended
 Items (Candidates) Ranker Trainer Events
 (imp, click, etc) LINE App User ID Items Model 
 parameter Item Request Top k items 
 for each user
16. Ranker Item A 0.7 Current Expected 
 Score 0.4 Current Expected 
 Score 0.6 Current Expected 
 Score 0.1 Current Expected 
 Score Item B Item C Item D > Ranker chooses an item from candidates A, B, C … by using contextual bandits > Each expected score is computed by a prediction model corresponding to the item
17. Prediction Model > Imp: 0.5, Click: 1.0, Mute: 0.0 > Balance Exploration-Exploitation Tradeoff > Laplace Approximation Bayesian Factorization Machine (FM) as an Arm of Contextual Bandits Output User ID Item ID User Features
 (Gender, Age, …) Other Features
 (Timestamp, …) Bayesian FM Embedding Embedding
18. Parameter Server for Distributed ML Events LINE App Trainer Worker Model Worker Model Parameter Server Ranker Executor Model Executor Model Δw W W Request Contents
19. Example of asynchronous communications between the parameter server and trainers. In the situation, learning doesn't work well just by accumulating the gradient in the parameter server. Asynchronous Distributed Online Learning
20. Asynchronous distributed learning algorithm Example of asynchronous communications between the parameter server and trainers. In the situation, learning doesn't work well just by accumulating the gradient in the parameter server. Asynchronous Distributed Online Learning Deceleration Backtrack
21. Storage for Parameters Item
 Embedding Parameter Server User
 Embedding Trainer Bayesian FM Events
22. Platform for Data Analysis
23. Primary Performance Metric > Consistent with user satisfaction trends obtained from questionnaire research > Easy to calculate > Stable under temporary fluctuations due to user's unfamiliarity Why score is used as main indicator?
24. Primary Performance Metric > Consistent with user satisfaction trends obtained from questionnaire research > Easy to calculate > Stable under temporary fluctuations due to user's unfamiliarity Why score is used as main indicator? Release new types of contents, or expand target users
25. Dashboard Country: JP
26. Anomaly Detection Country: JP
27. Offline Test Off-policy Evaluation We use the More Robust Doubly Robust (MRDR) algorithm to estimate the performance of a new logic from the data generated by other logics. Framework of Offline Test To Evaluate New Logic Offline Test Environment Parameter server and trainers are clones of the production system. We use the event logs stored in DataLake by using PySpark. Trainer Parameter Server (Offline) Ranker DataLake
28. A/B Test Country: JP
29. Experiments
30. Recent Experiments To Improve Recommendation Successful Experiments Incorporate Images in Banner User and Item embeddings LinUCB to Bayesian FM
31. LinUCB To Bayesian FM CTR +4.8% Score +5.8% -1.0% xCTR > Linearity: Easy To Parallelize LinUCB > Explicit Feature Interactions Bayesian FM
32. Incorporate Images in Banner
33. Incorporate Images in Banner CTR +56% Score +16% xCTR +35%
34. User and Item Embeddings 16 User ID Item ID User Features
 (Gender, Age, …) Other Features
 (Timestamp, …) Bayesian FM Embedding Embedding
35. User and Item Embeddings CTR +5.1% Score +25.3% xCTR -16.2%
36. Future Work
37. Synergies Between Online and Offline Learning Systems Feed Contents Personalize
38. Improve Machine Learning Platform Country: JP GPUs on Kubernetes Unified Hadoop Cluster
39. Thank You