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103 lines
4.3 KiB
Markdown
103 lines
4.3 KiB
Markdown
Home Mixer
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==========
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Home Mixer is the main service used to construct and serve Twitter's Home Timelines. It currently
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powers:
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- For you - best Tweets from people you follow + recommended out-of-network content
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- Following - reverse chronological Tweets from people you follow
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- Lists - reverse chronological Tweets from List members
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Home Mixer is built on Product Mixer, our custom Scala framework that facilitates building
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feeds of content.
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## Overview
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The For You recommendation algorithm in Home Mixer involves the following stages:
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- Candidate Generation - fetch Tweets from various Candidate Sources. For example:
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- Earlybird Search Index
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- User Tweet Entity Graph
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- Cr Mixer
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- Follow Recommendations Service
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- Feature Hydration
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- Fetch the ~6000 features needed for ranking
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- Scoring and Ranking using ML model
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- Filters and Heuristics. For example:
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- Author Diversity
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- Content Balance (In network vs Out of Network)
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- Feedback fatigue
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- Deduplication / previously seen Tweets removal
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- Visibility Filtering (blocked, muted authors/tweets, NSFW settings)
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- Mixing - integrate Tweets with non-Tweet content
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- Ads
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- Who-to-follow modules
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- Prompts
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- Product Features and Serving
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- Conversation Modules for replies
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- Social Context
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- Timeline Navigation
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- Edited Tweets
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- Feedback options
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- Pagination and cursoring
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- Observability and logging
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- Client instructions and content marshalling
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## Pipeline Structure
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### General
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Product Mixer services like Home Mixer are structured around Pipelines that split the execution
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into transparent and structured steps.
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Requests first go to Product Pipelines, which are used to select which Mixer Pipeline or
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Recommendation Pipeline to run for a given request. Each Mixer or Recommendation
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Pipeline may run multiple Candidate Pipelines to fetch candidates to include in the response.
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Mixer Pipelines combine the results of multiple heterogeneous Candidate Pipelines together
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(e.g. ads, tweets, users) while Recommendation Pipelines are used to score (via Scoring Pipelines)
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and rank the results of homogenous Candidate Pipelines so that the top-ranked ones can be returned.
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These pipelines also marshall candidates into a domain object and then into a transport object
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to return to the caller.
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Candidate Pipelines fetch candidates from underlying Candidate Sources and perform some basic
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operations on the Candidates, such as filtering out unwanted candidates, applying decorations,
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and hydrating features.
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The sections below describe the high-level pipeline structure (non-exhaustive) for the main Home
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Timeline tabs powered by Home Mixer.
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### For You
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- ForYouProductPipelineConfig
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- ForYouScoredTweetsMixerPipelineConfig (main orchestration layer - mixes Tweets with ads and users)
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- ForYouScoredTweetsCandidatePipelineConfig (fetch Tweets)
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- ScoredTweetsRecommendationPipelineConfig (main Tweet recommendation layer)
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- Fetch Tweet Candidates
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- ScoredTweetsInNetworkCandidatePipelineConfig
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- ScoredTweetsCrMixerCandidatePipelineConfig
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- ScoredTweetsUtegCandidatePipelineConfig
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- ScoredTweetsFrsCandidatePipelineConfig
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- Feature Hydration and Scoring
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- ScoredTweetsScoringPipelineConfig
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- ForYouConversationServiceCandidatePipelineConfig (backup reverse chron pipeline in case Scored Tweets fails)
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- ForYouAdsCandidatePipelineConfig (fetch ads)
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- ForYouWhoToFollowCandidatePipelineConfig (fetch users to recommend)
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### Following
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- FollowingProductPipelineConfig
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- FollowingMixerPipelineConfig
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- FollowingEarlybirdCandidatePipelineConfig (fetch tweets from Search Index)
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- ConversationServiceCandidatePipelineConfig (fetch ancestors for conversation modules)
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- FollowingAdsCandidatePipelineConfig (fetch ads)
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- FollowingWhoToFollowCandidatePipelineConfig (fetch users to recommend)
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### Lists
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- ListTweetsProductPipelineConfig
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- ListTweetsMixerPipelineConfig
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- ListTweetsTimelineServiceCandidatePipelineConfig (fetch tweets from timeline service)
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- ConversationServiceCandidatePipelineConfig (fetch ancestors for conversation modules)
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- ListTweetsAdsCandidatePipelineConfig (fetch ads)
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