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the-algorithm/pushservice/README.md

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Pushservice

Pushservice is the main push recommendation service at Twitter used to generate recommendation-based notifications for users. It currently powers two functionalities:

  • RefreshForPushHandler: This handler determines whether to send a recommendation push to a user based on their ID. It generates the best push recommendation item and coordinates with downstream services to deliver it
  • SendHandler: This handler determines and manage whether send the push to users based on the given target user details and the provided push recommendation item

Overview

RefreshForPushHandler

RefreshForPushHandler follows these steps:

  • Building Target and checking eligibility
    • Builds a target user object based on the given user ID
    • Performs target-level filterings to determine if the target is eligible for a recommendation push
  • Fetch Candidates
    • Retrieves a list of potential candidates for the push by querying various candidate sources using the target
  • Candidate Hydration
    • Hydrates the candidate details with batch calls to different downstream services
  • Pre-rank Filtering, also called Light Filtering
    • Filters the hydrated candidates with lightweight RPC calls
  • Rank
    • Perform feature hydration for candidates and target user
    • Performs light ranking on candidates
    • Performs heavy ranking on candidates
  • Take Step, also called Heavy Filtering
    • Takes the top-ranked candidates one by one and applies heavy filtering until one candidate passes all filter steps
  • Send
    • Calls the appropriate downstream service to deliver the eligible candidate as a push and in-app notification to the target user

SendHandler

SendHandler follows these steps:

  • Building Target
    • Builds a target user object based on the given user ID
  • Candidate Hydration
    • Hydrates the candidate details with batch calls to different downstream services
  • Feature Hydration
    • Perform feature hydration for candidates and target user
  • Take Step, also called Heavy Filtering
    • Perform filterings and validation checking for the given candidate
  • Send
    • Calls the appropriate downstream service to deliver the given candidate as a push and/or in-app notification to the target user