Add cold-start follow recommendations (#15945)

db/migrate/20210322164601_create_account_summaries.rb

@@ -0,0 +1,9 @@
+class CreateAccountSummaries < ActiveRecord::Migration[5.2]
+  def change
+    create_view :account_summaries, materialized: true
+
+    # To be able to refresh the view concurrently,
+    # at least one unique index is required
+    safety_assured { add_index :account_summaries, :account_id, unique: true }
+  end
+end

db/migrate/20210323114347_create_follow_recommendations.rb

@@ -0,0 +1,5 @@
+class CreateFollowRecommendations < ActiveRecord::Migration[5.2]
+  def change
+    create_view :follow_recommendations
+  end
+end

db/migrate/20210324171613_create_follow_recommendation_suppressions.rb

@@ -0,0 +1,9 @@
+class CreateFollowRecommendationSuppressions < ActiveRecord::Migration[6.1]
+  def change
+    create_table :follow_recommendation_suppressions do |t|
+      t.references :account, null: false, foreign_key: { on_delete: :cascade }, index: { unique: true }
+
+      t.timestamps
+    end
+  end
+end

db/schema.rb

@@ -2,15 +2,15 @@
 # of editing this file, please use the migrations feature of Active Record to
 # incrementally modify your database, and then regenerate this schema definition.
 #
-# Note that this schema.rb definition is the authoritative source for your
-# database schema. If you need to create the application database on another
-# system, you should be using db:schema:load, not running all the migrations
-# from scratch. The latter is a flawed and unsustainable approach (the more migrations
-# you'll amass, the slower it'll run and the greater likelihood for issues).
+# This file is the source Rails uses to define your schema when running `bin/rails
+# db:schema:load`. When creating a new database, `bin/rails db:schema:load` tends to
+# be faster and is potentially less error prone than running all of your
+# migrations from scratch. Old migrations may fail to apply correctly if those
+# migrations use external dependencies or application code.
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 2021_03_08_133107) do
+ActiveRecord::Schema.define(version: 2021_03_24_171613) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -406,6 +406,13 @@ ActiveRecord::Schema.define(version: 2021_03_08_133107) do
     t.index ["tag_id"], name: "index_featured_tags_on_tag_id"
   end
 
+  create_table "follow_recommendation_suppressions", force: :cascade do |t|
+    t.bigint "account_id", null: false
+    t.datetime "created_at", precision: 6, null: false
+    t.datetime "updated_at", precision: 6, null: false
+    t.index ["account_id"], name: "index_follow_recommendation_suppressions_on_account_id", unique: true
+  end
+
   create_table "follow_requests", force: :cascade do |t|
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
@@ -996,6 +1003,7 @@ ActiveRecord::Schema.define(version: 2021_03_08_133107) do
   add_foreign_key "favourites", "statuses", name: "fk_b0e856845e", on_delete: :cascade
   add_foreign_key "featured_tags", "accounts", on_delete: :cascade
   add_foreign_key "featured_tags", "tags", on_delete: :cascade
+  add_foreign_key "follow_recommendation_suppressions", "accounts", on_delete: :cascade
   add_foreign_key "follow_requests", "accounts", column: "target_account_id", name: "fk_9291ec025d", on_delete: :cascade
   add_foreign_key "follow_requests", "accounts", name: "fk_76d644b0e7", on_delete: :cascade
   add_foreign_key "follows", "accounts", column: "target_account_id", name: "fk_745ca29eac", on_delete: :cascade
@@ -1079,4 +1087,47 @@ ActiveRecord::Schema.define(version: 2021_03_08_133107) do
   SQL
   add_index "instances", ["domain"], name: "index_instances_on_domain", unique: true
 
+  create_view "account_summaries", materialized: true, sql_definition: <<-SQL
+      SELECT accounts.id AS account_id,
+      mode() WITHIN GROUP (ORDER BY t0.language) AS language,
+      mode() WITHIN GROUP (ORDER BY t0.sensitive) AS sensitive
+     FROM (accounts
+       CROSS JOIN LATERAL ( SELECT statuses.account_id,
+              statuses.language,
+              statuses.sensitive
+             FROM statuses
+            WHERE ((statuses.account_id = accounts.id) AND (statuses.deleted_at IS NULL))
+            ORDER BY statuses.id DESC
+           LIMIT 20) t0)
+    WHERE ((accounts.suspended_at IS NULL) AND (accounts.silenced_at IS NULL) AND (accounts.moved_to_account_id IS NULL) AND (accounts.discoverable = true) AND (accounts.locked = false))
+    GROUP BY accounts.id;
+  SQL
+  add_index "account_summaries", ["account_id"], name: "index_account_summaries_on_account_id", unique: true
+
+  create_view "follow_recommendations", sql_definition: <<-SQL
+      SELECT t0.account_id,
+      sum(t0.rank) AS rank,
+      array_agg(t0.reason) AS reason
+     FROM ( SELECT accounts.id AS account_id,
+              ((count(follows.id))::numeric / (1.0 + (count(follows.id))::numeric)) AS rank,
+              'most_followed'::text AS reason
+             FROM ((follows
+               JOIN accounts ON ((accounts.id = follows.target_account_id)))
+               JOIN users ON ((users.account_id = follows.account_id)))
+            WHERE ((users.current_sign_in_at >= (now() - 'P30D'::interval)) AND (accounts.suspended_at IS NULL) AND (accounts.moved_to_account_id IS NULL) AND (accounts.silenced_at IS NULL) AND (accounts.locked = false) AND (accounts.discoverable = true))
+            GROUP BY accounts.id
+           HAVING (count(follows.id) >= 5)
+          UNION ALL
+           SELECT accounts.id AS account_id,
+              (sum((status_stats.reblogs_count + status_stats.favourites_count)) / (1.0 + sum((status_stats.reblogs_count + status_stats.favourites_count)))) AS rank,
+              'most_interactions'::text AS reason
+             FROM ((status_stats
+               JOIN statuses ON ((statuses.id = status_stats.status_id)))
+               JOIN accounts ON ((accounts.id = statuses.account_id)))
+            WHERE ((statuses.id >= (((date_part('epoch'::text, (now() - 'P30D'::interval)) * (1000)::double precision))::bigint << 16)) AND (accounts.suspended_at IS NULL) AND (accounts.moved_to_account_id IS NULL) AND (accounts.silenced_at IS NULL) AND (accounts.locked = false) AND (accounts.discoverable = true))
+            GROUP BY accounts.id
+           HAVING (sum((status_stats.reblogs_count + status_stats.favourites_count)) >= (5)::numeric)) t0
+    GROUP BY t0.account_id
+    ORDER BY (sum(t0.rank)) DESC;
+  SQL
 end

db/views/account_summaries_v01.sql

@@ -0,0 +1,22 @@
+SELECT
+  accounts.id AS account_id,
+  mode() WITHIN GROUP (ORDER BY language ASC) AS language,
+  mode() WITHIN GROUP (ORDER BY sensitive ASC) AS sensitive
+FROM accounts
+CROSS JOIN LATERAL (
+  SELECT
+    statuses.account_id,
+    statuses.language,
+    statuses.sensitive
+  FROM statuses
+  WHERE statuses.account_id = accounts.id
+    AND statuses.deleted_at IS NULL
+  ORDER BY statuses.id DESC
+  LIMIT 20
+) t0
+WHERE accounts.suspended_at IS NULL
+  AND accounts.silenced_at IS NULL
+  AND accounts.moved_to_account_id IS NULL
+  AND accounts.discoverable = 't'
+  AND accounts.locked = 'f'
+GROUP BY accounts.id

db/views/follow_recommendations_v01.sql

@@ -0,0 +1,38 @@
+SELECT
+  account_id,
+  sum(rank) AS rank,
+  array_agg(reason) AS reason
+FROM (
+  SELECT
+    accounts.id AS account_id,
+    count(follows.id) / (1.0 + count(follows.id)) AS rank,
+    'most_followed' AS reason
+  FROM follows
+  INNER JOIN accounts ON accounts.id = follows.target_account_id
+  INNER JOIN users ON users.account_id = follows.account_id
+  WHERE users.current_sign_in_at >= (now() - interval '30 days')
+    AND accounts.suspended_at IS NULL
+    AND accounts.moved_to_account_id IS NULL
+    AND accounts.silenced_at IS NULL
+    AND accounts.locked = 'f'
+    AND accounts.discoverable = 't'
+  GROUP BY accounts.id
+  HAVING count(follows.id) >= 5
+  UNION ALL
+  SELECT accounts.id AS account_id,
+         sum(reblogs_count + favourites_count) / (1.0 + sum(reblogs_count + favourites_count)) AS rank,
+         'most_interactions' AS reason
+  FROM status_stats
+  INNER JOIN statuses ON statuses.id = status_stats.status_id
+  INNER JOIN accounts ON accounts.id = statuses.account_id
+  WHERE statuses.id >= ((date_part('epoch', now() - interval '30 days') * 1000)::bigint << 16)
+    AND accounts.suspended_at IS NULL
+    AND accounts.moved_to_account_id IS NULL
+    AND accounts.silenced_at IS NULL
+    AND accounts.locked = 'f'
+    AND accounts.discoverable = 't'
+  GROUP BY accounts.id
+  HAVING sum(reblogs_count + favourites_count) >= 5
+) t0
+GROUP BY account_id
+ORDER BY rank DESC