Change trending statuses to only show one status from each account (#18181)

Calculate trends in temporary sets to avoid having to manage items
that go below the decay threshold while not having any moments
where a half-processed set is accessible to end-users

4 files changed, 81 insertions, 82 deletions

diff --git a/app/models/trends/base.rb b/app/models/trends/base.rb
index 200f8d635..047111248 100644
--- a/app/models/trends/base.rb
+++ b/app/models/trends/base.rb
@@ -64,33 +64,38 @@ class Trends::Base
     redis.expire(used_key(at_time), 1.day.seconds)
   end
 
-  def trim_older_items
-    redis.zremrangebyscore("#{key_prefix}:all", '-inf', '(0.3')
-    redis.zremrangebyscore("#{key_prefix}:allowed", '-inf', '(0.3')
-  end
-
   def score_at_rank(rank)
     redis.zrevrange("#{key_prefix}:allowed", 0, rank, with_scores: true).last&.last || 0
   end
 
-  # @param [Integer] id
-  # @param [Float] score
-  # @param [Hash<String, Boolean>] subsets
-  def add_to_and_remove_from_subsets(id, score, subsets = {})
-    subsets.each_key do |subset|
-      key = [key_prefix, subset].compact.join(':')
+  def replace_items(suffix, items)
+    tmp_prefix    = "#{key_prefix}:tmp:#{SecureRandom.alphanumeric(6)}#{suffix}"
+    allowed_items = filter_for_allowed_items(items)
+
+    redis.pipelined do |pipeline|
+      items.each { |item| pipeline.zadd("#{tmp_prefix}:all", item[:score], item[:item].id) }
+      allowed_items.each { |item| pipeline.zadd("#{tmp_prefix}:allowed", item[:score], item[:item].id) }
 
-      if score.positive? && subsets[subset]
-        redis.zadd(key, score, id)
-      else
-        redis.zrem(key, id)
-      end
+      rename_set(pipeline, "#{tmp_prefix}:all", "#{key_prefix}:all#{suffix}", items)
+      rename_set(pipeline, "#{tmp_prefix}:allowed", "#{key_prefix}:allowed#{suffix}", allowed_items)
     end
   end
 
+  def filter_for_allowed_items(items)
+    raise NotImplementedError
+  end
+
   private
 
   def used_key(at_time)
     "#{key_prefix}:used:#{at_time.beginning_of_day.to_i}"
   end
+
+  def rename_set(pipeline, from_key, to_key, set_items)
+    if set_items.empty?
+      pipeline.del(to_key)
+    else
+      pipeline.rename(from_key, to_key)
+    end
+  end
 end
diff --git a/app/models/trends/links.rb b/app/models/trends/links.rb
index 5f046643a..604894cd6 100644
--- a/app/models/trends/links.rb
+++ b/app/models/trends/links.rb
@@ -8,14 +8,15 @@ class Trends::Links < Trends::Base
     review_threshold: 3,
     max_score_cooldown: 2.days.freeze,
     max_score_halflife: 8.hours.freeze,
+    decay_threshold: 1,
   }
 
   def register(status, at_time = Time.now.utc)
-    original_status = status.reblog? ? status.reblog : status
+    original_status = status.proper
 
-    return unless original_status.public_visibility? && status.public_visibility? &&
-                  !original_status.account.silenced? && !status.account.silenced? &&
-                  !original_status.spoiler_text?
+    return unless (original_status.public_visibility? && status.public_visibility?) &&
+                  !(original_status.account.silenced? || status.account.silenced?) &&
+                  !(original_status.spoiler_text? || original_status.sensitive?)
 
     original_status.preview_cards.each do |preview_card|
       add(preview_card, status.account_id, at_time) if preview_card.appropriate_for_trends?
@@ -61,6 +62,9 @@ class Trends::Links < Trends::Base
   private
 
   def calculate_scores(preview_cards, at_time)
+    global_items = []
+    locale_items = Hash.new { |h, key| h[key] = [] }
+
     preview_cards.each do |preview_card|
       expected  = preview_card.history.get(at_time - 1.day).accounts.to_f
       expected  = 1.0 if expected.zero?
@@ -87,33 +91,23 @@ class Trends::Links < Trends::Base
 
       decaying_score = max_score * (0.5**((at_time.to_f - max_time.to_f) / options[:max_score_halflife].to_f))
 
-      add_to_and_remove_from_subsets(preview_card.id, decaying_score, {
-        all: true,
-        allowed: preview_card.trendable?,
-      })
-
-      next unless valid_locale?(preview_card.language)
+      next unless decaying_score >= options[:decay_threshold]
 
-      add_to_and_remove_from_subsets(preview_card.id, decaying_score, {
-        "all:#{preview_card.language}" => true,
-        "allowed:#{preview_card.language}" => preview_card.trendable?,
-      })
+      global_items << { score: decaying_score, item:  preview_card }
+      locale_items[preview_card.language] << { score: decaying_score, item: preview_card } if valid_locale?(preview_card.language)
     end
 
-    trim_older_items
-
-    # Clean up localized sets by calculating the intersection with the main
-    # set. We do this instead of just deleting the localized sets to avoid
-    # having moments where the API returns empty results
+    replace_items('', global_items)
 
-    redis.pipelined do
-      Trends.available_locales.each do |locale|
-        redis.zinterstore("#{key_prefix}:all:#{locale}", ["#{key_prefix}:all:#{locale}", "#{key_prefix}:all"], aggregate: 'max')
-        redis.zinterstore("#{key_prefix}:allowed:#{locale}", ["#{key_prefix}:allowed:#{locale}", "#{key_prefix}:allowed"], aggregate: 'max')
-      end
+    Trends.available_locales.each do |locale|
+      replace_items(":#{locale}", locale_items[locale])
     end
   end
 
+  def filter_for_allowed_items(items)
+    items.select { |item| item[:item].trendable? }
+  end
+
   def would_be_trending?(id)
     score(id) > score_at_rank(options[:review_threshold] - 1)
   end
diff --git a/app/models/trends/statuses.rb b/app/models/trends/statuses.rb
index 3013bc1d1..777065d3e 100644
--- a/app/models/trends/statuses.rb
+++ b/app/models/trends/statuses.rb
@@ -7,6 +7,7 @@ class Trends::Statuses < Trends::Base
     threshold: 5,
     review_threshold: 3,
     score_halflife: 2.hours.freeze,
+    decay_threshold: 0.3,
   }
 
   class Query < Trends::Query
@@ -31,7 +32,7 @@ class Trends::Statuses < Trends::Base
   end
 
   def register(status, at_time = Time.now.utc)
-    add(status.proper, status.account_id, at_time) if eligible?(status)
+    add(status.proper, status.account_id, at_time) if eligible?(status.proper)
   end
 
   def add(status, _account_id, at_time = Time.now.utc)
@@ -74,53 +75,45 @@ class Trends::Statuses < Trends::Base
   private
 
   def eligible?(status)
-    original_status = status.proper
-
-    original_status.public_visibility? &&
-      original_status.account.discoverable? && !original_status.account.silenced? &&
-      original_status.spoiler_text.blank? && !original_status.sensitive? && !original_status.reply?
+    status.public_visibility? && status.account.discoverable? && !status.account.silenced? && status.spoiler_text.blank? && !status.sensitive? && !status.reply?
   end
 
   def calculate_scores(statuses, at_time)
-    redis.pipelined do
-      statuses.each do |status|
-        expected  = 1.0
-        observed  = (status.reblogs_count + status.favourites_count).to_f
-
-        score = begin
-          if expected > observed || observed < options[:threshold]
-            0
-          else
-            ((observed - expected)**2) / expected
-          end
+    global_items = []
+    locale_items = Hash.new { |h, key| h[key] = [] }
+
+    statuses.each do |status|
+      expected  = 1.0
+      observed  = (status.reblogs_count + status.favourites_count).to_f
+
+      score = begin
+        if expected > observed || observed < options[:threshold]
+          0
+        else
+          ((observed - expected)**2) / expected
         end
+      end
 
-        decaying_score = score * (0.5**((at_time.to_f - status.created_at.to_f) / options[:score_halflife].to_f))
+      decaying_score = score * (0.5**((at_time.to_f - status.created_at.to_f) / options[:score_halflife].to_f))
 
-        add_to_and_remove_from_subsets(status.id, decaying_score, {
-          all: true,
-          allowed: status.trendable? && status.account.discoverable?,
-        })
+      next unless decaying_score >= options[:decay_threshold]
 
-        next unless valid_locale?(status.language)
+      global_items << { score: decaying_score, item: status }
+      locale_items[status.language] << { account_id: status.account_id, score: decaying_score, item: status } if valid_locale?(status.language)
+    end
 
-        add_to_and_remove_from_subsets(status.id, decaying_score, {
-          "all:#{status.language}" => true,
-          "allowed:#{status.language}" => status.trendable? && status.account.discoverable?,
-        })
-      end
+    replace_items('', global_items)
 
-      trim_older_items
+    Trends.available_locales.each do |locale|
+      replace_items(":#{locale}", locale_items[locale])
+    end
+  end
 
-      # Clean up localized sets by calculating the intersection with the main
-      # set. We do this instead of just deleting the localized sets to avoid
-      # having moments where the API returns empty results
+  def filter_for_allowed_items(items)
+    # Show only one status per account, pick the one with the highest score
+    # that's also eligible to trend
 
-      Trends.available_locales.each do |locale|
-        redis.zinterstore("#{key_prefix}:all:#{locale}", ["#{key_prefix}:all:#{locale}", "#{key_prefix}:all"], aggregate: 'max')
-        redis.zinterstore("#{key_prefix}:allowed:#{locale}", ["#{key_prefix}:allowed:#{locale}", "#{key_prefix}:allowed"], aggregate: 'max')
-      end
-    end
+    items.group_by { |item| item[:account_id] }.values.filter_map { |account_items| account_items.select { |item| item[:item].trendable? && item[:item].account.discoverable? }.max_by { |item| item[:score] } }
   end
 
   def would_be_trending?(id)
diff --git a/app/models/trends/tags.rb b/app/models/trends/tags.rb
index 3caa58815..19ade52ba 100644
--- a/app/models/trends/tags.rb
+++ b/app/models/trends/tags.rb
@@ -8,6 +8,7 @@ class Trends::Tags < Trends::Base
     review_threshold: 3,
     max_score_cooldown: 2.days.freeze,
     max_score_halflife: 4.hours.freeze,
+    decay_threshold: 1,
   }
 
   def register(status, at_time = Time.now.utc)
@@ -26,7 +27,6 @@ class Trends::Tags < Trends::Base
   def refresh(at_time = Time.now.utc)
     tags = Tag.where(id: (recently_used_ids(at_time) + currently_trending_ids(false, -1)).uniq)
     calculate_scores(tags, at_time)
-    trim_older_items
   end
 
   def request_review
@@ -53,6 +53,8 @@ class Trends::Tags < Trends::Base
   private
 
   def calculate_scores(tags, at_time)
+    items = []
+
     tags.each do |tag|
       expected  = tag.history.get(at_time - 1.day).accounts.to_f
       expected  = 1.0 if expected.zero?
@@ -79,11 +81,16 @@ class Trends::Tags < Trends::Base
 
       decaying_score = max_score * (0.5**((at_time.to_f - max_time.to_f) / options[:max_score_halflife].to_f))
 
-      add_to_and_remove_from_subsets(tag.id, decaying_score, {
-        all: true,
-        allowed: tag.trendable?,
-      })
+      next unless decaying_score >= options[:decay_threshold]
+
+      items << { score: decaying_score, item: tag }
     end
+
+    replace_items('', items)
+  end
+
+  def filter_for_allowed_items(items)
+    items.select { |item| item[:item].trendable? }
   end
 
   def would_be_trending?(id)