Fix performance of home feed regeneration (#12084)

Fetching statuses from all followed accounts at once takes too long
within Postgres. Fetching them one by one and merging in Ruby
could be a lot less resource-intensive

Because the query for dynamically fetching the home timeline is so
heavy, we can no longer offer it when the home timeline is missing

11 files changed, 130 insertions, 95 deletions

diff --git a/app/controllers/api/v1/timelines/home_controller.rb b/app/controllers/api/v1/timelines/home_controller.rb
index fcd0757f1..ff5ede138 100644
--- a/app/controllers/api/v1/timelines/home_controller.rb
+++ b/app/controllers/api/v1/timelines/home_controller.rb
@@ -13,7 +13,7 @@ class Api::V1::Timelines::HomeController < Api::BaseController
     render json: @statuses,
            each_serializer: REST::StatusSerializer,
            relationships: StatusRelationshipsPresenter.new(@statuses, current_user&.account_id),
-           status: regeneration_in_progress? ? 206 : 200
+           status: account_home_feed.regenerating? ? 206 : 200
   end
 
   private
@@ -62,8 +62,4 @@ class Api::V1::Timelines::HomeController < Api::BaseController
   def pagination_since_id
     @statuses.first.id
   end
-
-  def regeneration_in_progress?
-    Redis.current.exists("account:#{current_account.id}:regeneration")
-  end
 end
diff --git a/app/javascript/mastodon/actions/timelines.js b/app/javascript/mastodon/actions/timelines.js
index 7eeba2aa7..bc2ac5e82 100644
--- a/app/javascript/mastodon/actions/timelines.js
+++ b/app/javascript/mastodon/actions/timelines.js
@@ -97,7 +97,7 @@ export function expandTimeline(timelineId, path, params = {}, done = noOp) {
     api(getState).get(path, { params }).then(response => {
       const next = getLinks(response).refs.find(link => link.rel === 'next');
       dispatch(importFetchedStatuses(response.data));
-      dispatch(expandTimelineSuccess(timelineId, response.data, next ? next.uri : null, response.code === 206, isLoadingRecent, isLoadingMore, isLoadingRecent && preferPendingItems));
+      dispatch(expandTimelineSuccess(timelineId, response.data, next ? next.uri : null, response.status === 206, isLoadingRecent, isLoadingMore, isLoadingRecent && preferPendingItems));
       done();
     }).catch(error => {
       dispatch(expandTimelineFail(timelineId, error, isLoadingMore));
diff --git a/app/javascript/mastodon/components/missing_indicator.js b/app/javascript/mastodon/components/missing_indicator.js
index 70d8c3b98..7b0101bab 100644
--- a/app/javascript/mastodon/components/missing_indicator.js
+++ b/app/javascript/mastodon/components/missing_indicator.js
@@ -1,17 +1,24 @@
 import React from 'react';
+import PropTypes from 'prop-types';
 import { FormattedMessage } from 'react-intl';
+import illustration from 'mastodon/../images/elephant_ui_disappointed.svg';
+import classNames from 'classnames';
 
-const MissingIndicator = () => (
-  <div className='regeneration-indicator missing-indicator'>
-    <div>
-      <div className='regeneration-indicator__figure' />
+const MissingIndicator = ({ fullPage }) => (
+  <div className={classNames('regeneration-indicator', { 'regeneration-indicator--without-header': fullPage })}>
+    <div className='regeneration-indicator__figure'>
+      <img src={illustration} alt='' />
+    </div>
 
-      <div className='regeneration-indicator__label'>
-        <FormattedMessage id='missing_indicator.label' tagName='strong' defaultMessage='Not found' />
-        <FormattedMessage id='missing_indicator.sublabel' defaultMessage='This resource could not be found' />
-      </div>
+    <div className='regeneration-indicator__label'>
+      <FormattedMessage id='missing_indicator.label' tagName='strong' defaultMessage='Not found' />
+      <FormattedMessage id='missing_indicator.sublabel' defaultMessage='This resource could not be found' />
     </div>
   </div>
 );
 
+MissingIndicator.propTypes = {
+  fullPage: PropTypes.bool,
+};
+
 export default MissingIndicator;
diff --git a/app/javascript/mastodon/components/regeneration_indicator.js b/app/javascript/mastodon/components/regeneration_indicator.js
new file mode 100644
index 000000000..faf88c6b5
--- /dev/null
+++ b/app/javascript/mastodon/components/regeneration_indicator.js
@@ -0,0 +1,18 @@
+import React from 'react';
+import { FormattedMessage } from 'react-intl';
+import illustration from 'mastodon/../images/elephant_ui_working.svg';
+
+const MissingIndicator = () => (
+  <div className='regeneration-indicator'>
+    <div className='regeneration-indicator__figure'>
+      <img src={illustration} alt='' />
+    </div>
+
+    <div className='regeneration-indicator__label'>
+      <FormattedMessage id='regeneration_indicator.label' tagName='strong' defaultMessage='Loading&hellip;' />
+      <FormattedMessage id='regeneration_indicator.sublabel' defaultMessage='Your home feed is being prepared!' />
+    </div>
+  </div>
+);
+
+export default MissingIndicator;
diff --git a/app/javascript/mastodon/components/status_list.js b/app/javascript/mastodon/components/status_list.js
index 745e6422d..e1b370c91 100644
--- a/app/javascript/mastodon/components/status_list.js
+++ b/app/javascript/mastodon/components/status_list.js
@@ -1,12 +1,12 @@
 import { debounce } from 'lodash';
 import React from 'react';
-import { FormattedMessage } from 'react-intl';
 import ImmutablePropTypes from 'react-immutable-proptypes';
 import PropTypes from 'prop-types';
 import StatusContainer from '../containers/status_container';
 import ImmutablePureComponent from 'react-immutable-pure-component';
 import LoadGap from './load_gap';
 import ScrollableList from './scrollable_list';
+import RegenerationIndicator from 'mastodon/components/regeneration_indicator';
 
 export default class StatusList extends ImmutablePureComponent {
 
@@ -81,18 +81,7 @@ export default class StatusList extends ImmutablePureComponent {
     const { isLoading, isPartial } = other;
 
     if (isPartial) {
-      return (
-        <div className='regeneration-indicator'>
-          <div>
-            <div className='regeneration-indicator__figure' />
-
-            <div className='regeneration-indicator__label'>
-              <FormattedMessage id='regeneration_indicator.label' tagName='strong' defaultMessage='Loading&hellip;' />
-              <FormattedMessage id='regeneration_indicator.sublabel' defaultMessage='Your home feed is being prepared!' />
-            </div>
-          </div>
-        </div>
-      );
+      return <RegenerationIndicator />;
     }
 
     let scrollableContent = (isLoading || statusIds.size > 0) ? (
diff --git a/app/javascript/mastodon/features/generic_not_found/index.js b/app/javascript/mastodon/features/generic_not_found/index.js
index 0290be47f..41cd61a5f 100644
--- a/app/javascript/mastodon/features/generic_not_found/index.js
+++ b/app/javascript/mastodon/features/generic_not_found/index.js
@@ -4,7 +4,7 @@ import MissingIndicator from '../../components/missing_indicator';
 
 const GenericNotFound = () => (
   <Column>
-    <MissingIndicator />
+    <MissingIndicator fullPage />
   </Column>
 );
 
diff --git a/app/javascript/styles/mastodon/components.scss b/app/javascript/styles/mastodon/components.scss
index a6675b8ed..d9182ade9 100644
--- a/app/javascript/styles/mastodon/components.scss
+++ b/app/javascript/styles/mastodon/components.scss
@@ -3127,37 +3127,27 @@ a.status-card.compact:hover {
   cursor: default;
   display: flex;
   flex: 1 1 auto;
+  flex-direction: column;
   align-items: center;
   justify-content: center;
   padding: 20px;
 
-  & > div {
-    width: 100%;
-    background: transparent;
-    padding-top: 0;
-  }
-
   &__figure {
-    background: url('../images/elephant_ui_working.svg') no-repeat center 0;
-    width: 100%;
-    height: 160px;
-    background-size: contain;
-    position: absolute;
-    top: 50%;
-    left: 50%;
-    transform: translate(-50%, -50%);
+    &,
+    img {
+      display: block;
+      width: auto;
+      height: 160px;
+      margin: 0;
+    }
   }
 
-  &.missing-indicator {
+  &--without-header {
     padding-top: 20px + 48px;
-
-    .regeneration-indicator__figure {
-      background-image: url('../images/elephant_ui_disappointed.svg');
-    }
   }
 
   &__label {
-    margin-top: 200px;
+    margin-top: 30px;
 
     strong {
       display: block;
diff --git a/app/javascript/styles/mastodon/introduction.scss b/app/javascript/styles/mastodon/introduction.scss
index 222d8f60e..b44ae7306 100644
--- a/app/javascript/styles/mastodon/introduction.scss
+++ b/app/javascript/styles/mastodon/introduction.scss
@@ -3,9 +3,10 @@
   flex-direction: column;
   justify-content: center;
   align-items: center;
+  height: 100vh;
+  background: $ui-base-color;
 
   @media screen and (max-width: 920px) {
-    background: darken($ui-base-color, 8%);
     display: block !important;
   }
 
diff --git a/app/lib/feed_manager.rb b/app/lib/feed_manager.rb
index 871ec5c19..d8b486b60 100644
--- a/app/lib/feed_manager.rb
+++ b/app/lib/feed_manager.rb
@@ -19,7 +19,7 @@ class FeedManager
 
   def filter?(timeline_type, status, receiver_id)
     if timeline_type == :home
-      filter_from_home?(status, receiver_id)
+      filter_from_home?(status, receiver_id, build_crutches(receiver_id, [status]))
     elsif timeline_type == :mentions
       filter_from_mentions?(status, receiver_id)
     else
@@ -29,6 +29,7 @@ class FeedManager
 
   def push_to_home(account, status)
     return false unless add_to_feed(:home, account.id, status, account.user&.aggregates_reblogs?)
+
     trim(:home, account.id)
     PushUpdateWorker.perform_async(account.id, status.id, "timeline:#{account.id}") if push_update_required?("timeline:#{account.id}")
     true
@@ -36,6 +37,7 @@ class FeedManager
 
   def unpush_from_home(account, status)
     return false unless remove_from_feed(:home, account.id, status, account.user&.aggregates_reblogs?)
+
     redis.publish("timeline:#{account.id}", Oj.dump(event: :delete, payload: status.id.to_s))
     true
   end
@@ -46,7 +48,9 @@ class FeedManager
       should_filter &&= !ListAccount.where(list_id: list.id, account_id: status.in_reply_to_account_id).exists?
       return false if should_filter
     end
+
     return false unless add_to_feed(:list, list.id, status, list.account.user&.aggregates_reblogs?)
+
     trim(:list, list.id)
     PushUpdateWorker.perform_async(list.account_id, status.id, "timeline:list:#{list.id}") if push_update_required?("timeline:list:#{list.id}")
     true
@@ -54,6 +58,7 @@ class FeedManager
 
   def unpush_from_list(list, status)
     return false unless remove_from_feed(:list, list.id, status, list.account.user&.aggregates_reblogs?)
+
     redis.publish("timeline:list:#{list.id}", Oj.dump(event: :delete, payload: status.id.to_s))
     true
   end
@@ -85,16 +90,21 @@ class FeedManager
 
   def merge_into_timeline(from_account, into_account)
     timeline_key = key(:home, into_account.id)
-    query        = from_account.statuses.limit(FeedManager::MAX_ITEMS / 4)
+    aggregate    = into_account.user&.aggregates_reblogs?
+    query        = from_account.statuses.where(visibility: [:public, :unlisted, :private]).includes(:preloadable_poll, reblog: :account).limit(FeedManager::MAX_ITEMS / 4)
 
     if redis.zcard(timeline_key) >= FeedManager::MAX_ITEMS / 4
-      oldest_home_score = redis.zrange(timeline_key, 0, 0, with_scores: true)&.first&.last&.to_i || 0
+      oldest_home_score = redis.zrange(timeline_key, 0, 0, with_scores: true).first.last.to_i
       query = query.where('id > ?', oldest_home_score)
     end
 
-    query.each do |status|
-      next if status.direct_visibility? || status.limited_visibility? || filter?(:home, status, into_account)
-      add_to_feed(:home, into_account.id, status, into_account.user&.aggregates_reblogs?)
+    statuses = query.to_a
+    crutches = build_crutches(into_account.id, statuses)
+
+    statuses.each do |status|
+      next if filter_from_home?(status, into_account, crutches)
+
+      add_to_feed(:home, into_account.id, status, aggregate)
     end
 
     trim(:home, into_account.id)
@@ -120,24 +130,35 @@ class FeedManager
   end
 
   def populate_feed(account)
-    added  = 0
-    limit  = FeedManager::MAX_ITEMS / 2
-    max_id = nil
+    limit        = FeedManager::MAX_ITEMS / 2
+    aggregate    = account.user&.aggregates_reblogs?
+    timeline_key = key(:home, account.id)
 
-    loop do
-      statuses = Status.as_home_timeline(account)
-                       .paginate_by_max_id(limit, max_id)
+    account.statuses.where.not(visibility: :direct).limit(limit).each do |status|
+      add_to_feed(:home, account.id, status, aggregate)
+    end
 
-      break if statuses.empty?
+    account.following.includes(:account_stat).find_each do |target_account|
+      if redis.zcard(timeline_key) >= limit
+        oldest_home_score = redis.zrange(timeline_key, 0, 0, with_scores: true).first.last.to_i
+        last_status_score = Mastodon::Snowflake.id_at(account.last_status_at)
 
-      statuses.each do |status|
-        next if filter_from_home?(status, account)
-        added += 1 if add_to_feed(:home, account.id, status, account.user&.aggregates_reblogs?)
+        # If the feed is full and this account has not posted more recently
+        # than the last item on the feed, then we can skip the whole account
+        # because none of its statuses would stay on the feed anyway
+        next if last_status_score < oldest_home_score
       end
 
-      break unless added.zero?
+      statuses = target_account.statuses.where(visibility: [:public, :unlisted, :private]).includes(:preloadable_poll, reblog: :account).limit(limit)
+      crutches = build_crutches(account.id, statuses)
+
+      statuses.each do |status|
+        next if filter_from_home?(status, account, crutches)
+
+        add_to_feed(:home, account.id, status, aggregate)
+      end
 
-      max_id = statuses.last.id
+      trim(:home, account.id)
     end
   end
 
@@ -152,31 +173,33 @@ class FeedManager
       (context == :home ? Mute.where(account_id: receiver_id, target_account_id: account_ids).any? : Mute.where(account_id: receiver_id, target_account_id: account_ids, hide_notifications: true).any?)
   end
 
-  def filter_from_home?(status, receiver_id)
+  def filter_from_home?(status, receiver_id, crutches)
     return false if receiver_id == status.account_id
     return true  if status.reply? && (status.in_reply_to_id.nil? || status.in_reply_to_account_id.nil?)
     return true  if phrase_filtered?(status, receiver_id, :home)
 
-    check_for_blocks = status.active_mentions.pluck(:account_id)
+    check_for_blocks = crutches[:active_mentions][status.id] || []
     check_for_blocks.concat([status.account_id])
 
     if status.reblog?
       check_for_blocks.concat([status.reblog.account_id])
-      check_for_blocks.concat(status.reblog.active_mentions.pluck(:account_id))
+      check_for_blocks.concat(crutches[:active_mentions][status.reblog_of_id] || [])
     end
 
-    return true if blocks_or_mutes?(receiver_id, check_for_blocks, :home)
+    return true if check_for_blocks.any? { |target_account_id| crutches[:blocking][target_account_id] || crutches[:muting][target_account_id] }
 
     if status.reply? && !status.in_reply_to_account_id.nil?                                                                      # Filter out if it's a reply
-      should_filter   = !Follow.where(account_id: receiver_id, target_account_id: status.in_reply_to_account_id).exists?         # and I'm not following the person it's a reply to
+      should_filter   = !crutches[:following][status.in_reply_to_account_id]                                                     # and I'm not following the person it's a reply to
       should_filter &&= receiver_id != status.in_reply_to_account_id                                                             # and it's not a reply to me
       should_filter &&= status.account_id != status.in_reply_to_account_id                                                       # and it's not a self-reply
-      return should_filter
+
+      return !!should_filter
     elsif status.reblog?                                                                                                         # Filter out a reblog
-      should_filter   = Follow.where(account_id: receiver_id, target_account_id: status.account_id, show_reblogs: false).exists? # if the reblogger's reblogs are suppressed
-      should_filter ||= Block.where(account_id: status.reblog.account_id, target_account_id: receiver_id).exists?                # or if the author of the reblogged status is blocking me
-      should_filter ||= AccountDomainBlock.where(account_id: receiver_id, domain: status.reblog.account.domain).exists?          # or the author's domain is blocked
-      return should_filter
+      should_filter   = crutches[:hiding_reblogs][status.account_id]                                                             # if the reblogger's reblogs are suppressed
+      should_filter ||= crutches[:blocked_by][status.reblog.account_id]                                                          # or if the author of the reblogged status is blocking me
+      should_filter ||= crutches[:domain_blocking][status.reblog.account.domain]                                                 # or the author's domain is blocked
+
+      return !!should_filter
     end
 
     false
@@ -308,4 +331,31 @@ class FeedManager
 
     redis.zrem(timeline_key, status.id)
   end
+
+  def build_crutches(receiver_id, statuses)
+    crutches = {}
+
+    crutches[:active_mentions] = Mention.active.where(status_id: statuses.flat_map { |s| [s.id, s.reblog_of_id] }.compact).pluck(:status_id, :account_id).each_with_object({}) { |(id, account_id), mapping| (mapping[id] ||= []).push(account_id) }
+
+    check_for_blocks = statuses.flat_map do |s|
+      arr = crutches[:active_mentions][s.id] || []
+      arr.concat([s.account_id])
+
+      if s.reblog?
+        arr.concat([s.reblog.account_id])
+        arr.concat(crutches[:active_mentions][s.reblog_of_id] || [])
+      end
+
+      arr
+    end
+
+    crutches[:following]       = Follow.where(account_id: receiver_id, target_account_id: statuses.map(&:in_reply_to_account_id).compact).pluck(:target_account_id).each_with_object({}) { |id, mapping| mapping[id] = true }
+    crutches[:hiding_reblogs]  = Follow.where(account_id: receiver_id, target_account_id: statuses.map { |s| s.account_id if s.reblog? }.compact, show_reblogs: false).pluck(:target_account_id).each_with_object({}) { |id, mapping| mapping[id] = true }
+    crutches[:blocking]        = Block.where(account_id: receiver_id, target_account_id: check_for_blocks).pluck(:target_account_id).each_with_object({}) { |id, mapping| mapping[id] = true }
+    crutches[:muting]          = Mute.where(account_id: receiver_id, target_account_id: check_for_blocks).pluck(:target_account_id).each_with_object({}) { |id, mapping| mapping[id] = true }
+    crutches[:domain_blocking] = AccountDomainBlock.where(account_id: receiver_id, domain: statuses.map { |s| s.reblog&.account&.domain }.compact).pluck(:domain).each_with_object({}) { |domain, mapping| mapping[domain] = true }
+    crutches[:blocked_by]      = Block.where(target_account_id: receiver_id, account_id: statuses.map { |s| s.reblog&.account_id }.compact).pluck(:account_id).each_with_object({}) { |id, mapping| mapping[id] = true }
+
+    crutches
+  end
 end
diff --git a/app/models/home_feed.rb b/app/models/home_feed.rb
index ba7564983..1fd506138 100644
--- a/app/models/home_feed.rb
+++ b/app/models/home_feed.rb
@@ -7,19 +7,7 @@ class HomeFeed < Feed
     @account = account
   end
 
-  def get(limit, max_id = nil, since_id = nil, min_id = nil)
-    if redis.exists("account:#{@account.id}:regeneration")
-      from_database(limit, max_id, since_id, min_id)
-    else
-      super
-    end
-  end
-
-  private
-
-  def from_database(limit, max_id, since_id, min_id)
-    Status.as_home_timeline(@account)
-          .paginate_by_id(limit, max_id: max_id, since_id: since_id, min_id: min_id)
-          .reject { |status| FeedManager.instance.filter?(:home, status, @account.id) }
+  def regenerating?
+    redis.exists("account:#{@id}:regeneration")
   end
 end
diff --git a/app/models/status.rb b/app/models/status.rb
index 3504ac370..0c01a5389 100644
--- a/app/models/status.rb
+++ b/app/models/status.rb
@@ -282,10 +282,6 @@ class Status < ApplicationRecord
       where(language: nil).or where(language: account.chosen_languages)
     end
 
-    def as_home_timeline(account)
-      where(account: [account] + account.following).where(visibility: [:public, :unlisted, :private])
-    end
-
     def as_public_timeline(account = nil, local_only = false)
       query = timeline_scope(local_only).without_replies