Feed algorithms

Every 5 minutes, Minds will trigger a job that gathers all the entities (activities, images, videos and blogs) that received any kind of vote in that interval. Then, it will update the total amount of votes on the ElasticSearch documents, which are used to display all the feeds and search results, for these entities.

Top Feed

When querying the Top Feed:

• Gather all the public activities that were created within the selected time period.

• Calculate the score using:

  magnitude = up + down
  
  score = ((up + 1.9208) / magnitude - 1.96 * SQRT((up * down) / magnitude + 0.9604) / magnitude) / (1 + 3.8416 / magnitude)

  where up is the total amount of up votes for that entity, down is the total amount of down votes for that entity.

• Sort all results from the highest score to the lowest

Channels and Groups

These special categories will still use the above algorithm but, once the list is built, it will transform the list by adding up the scores based on the activities' owner (Top Channels) or the container (Top Groups).

Hot Feed

Refer to the old implementation section.

Old Implementation

The, now deprecated, system was that every 5 minutes, Minds ran several jobs that gathered all the entities (activities, images, videos and blogs) that received any kind of vote in the last 12 hours, 24 hours, 7 days, 30 days and 1 year. Then it would store the amount of votes received in the time period for that entity.

Issues with this system:

• Computationally expensive on 30 days and 1 year periods.
• Old entities being wrongfully listed as Top/Hot on quieter moments in the site.

Top Feed

When querying the Top Feed:

• Gather all the public activities that have at least 1 vote and their up votes were synchronized for the selected period in the last 3 days.

• Calculate the score using:

  magnitude = up + down
  
  if magnitude <= 0:
      score = -10
  
  else:
      score = ((up + 1.9208) / magnitude - 1.96 * SQRT((up * down) / magnitude + 0.9604) / magnitude) / (1 + 3.8416 / magnitude)

  where up is the amount of up votes in the selected time period, down is the amount of down votes in the selected time period.

• Sort all results from the highest score to the lowest.

Hot Feed

When querying the Hot Feed:

• Gather all the public activities that have at least 1 vote and their up votes were synchronized for the selected period in the last 7 days.

• Calculate the score using:

  age = now - time_created - 1546300800;
  balance = up - down;
  order = LOG(MAX(ABS(balance), 1));
  
  if balance > 0:
      sign_of_balance = 1
  
  else if balance < 0:
      sign_of_balance = -1
  
  else:
      sign_of_balance = 0
  
  score = (sign_of_balance * order) - (age / 43200);

  where now is the current time, time_created is when the entity was posted onto Minds, 1546300800 is 1/1/2019 to calculate decay, up is the amount of up votes in the selected time period, down is the amount of down votes in the selected time period, and 43200 is 12 hours.

• Sort all results from the highest score to the lowest.