the-algorithm/pushservice/README.md

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