diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6f94ebea2..cfc95dcf6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,32 @@ Changelog
 
 All notable changes to this project will be documented in this file.
 
+## [3.2.2] - 2020-12-19
+### Added
+
+- Add `tootctl maintenance fix-duplicates` ([ThibG](https://github.com/tootsuite/mastodon/pull/14860), [Gargron](https://github.com/tootsuite/mastodon/pull/15223))
+  - Index corruption in the database?
+  - This command is for you
+
+### Removed
+
+- Remove dependency on unused and unmaintained http_parser.rb gem ([ThibG](https://github.com/tootsuite/mastodon/pull/14574))
+
+### Fixed
+
+- Fix Move handler not being triggered when failing to fetch target account ([ThibG](https://github.com/tootsuite/mastodon/pull/15107))
+- Fix downloading remote media files when server returns empty filename ([ThibG](https://github.com/tootsuite/mastodon/pull/14867))
+- Fix possible casing inconsistencies in hashtag search ([ThibG](https://github.com/tootsuite/mastodon/pull/14906))
+- Fix updating account counters when association is not yet created ([Gargron](https://github.com/tootsuite/mastodon/pull/15108))
+- Fix account processing failing because of large collections ([ThibG](https://github.com/tootsuite/mastodon/pull/15027))
+- Fix resolving an account through its non-canonical form (i.e. alternate domain) ([ThibG](https://github.com/tootsuite/mastodon/pull/15187))
+- Fix slow distinct queries where grouped queries are faster ([Gargron](https://github.com/tootsuite/mastodon/pull/15287))
+
+### Security
+
+- Fix 2FA/sign-in token sessions being valid after password change ([Gargron](https://github.com/tootsuite/mastodon/pull/14802))
+- Fix resolving accounts sometimes creating duplicate records for a given ActivityPub identifier ([ThibG](https://github.com/tootsuite/mastodon/pull/15364))
+
 ## [3.2.1] - 2020-10-19
 ### Added
 
diff --git a/Gemfile b/Gemfile
index 0891371be..5ac1c79c1 100644
--- a/Gemfile
+++ b/Gemfile
@@ -60,7 +60,6 @@ gem 'health_check', git: 'https://github.com/ianheggie/health_check', ref: '0b79
 gem 'htmlentities', '~> 4.3'
 gem 'http', '~> 4.4'
 gem 'http_accept_language', '~> 2.1'
-gem 'http_parser.rb', '~> 0.6', git: 'https://github.com/tmm1/http_parser.rb', ref: '54b17ba8c7d8d20a16dfc65d1775241833219cf2', submodules: true
 gem 'httplog', '~> 1.4.3'
 gem 'idn-ruby', require: 'idn'
 gem 'kaminari', '~> 1.2'
diff --git a/Gemfile.lock b/Gemfile.lock
index 62c20bf07..c3216870d 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -13,14 +13,6 @@ GIT
   specs:
     posix-spawn (0.3.13)
 
-GIT
-  remote: https://github.com/tmm1/http_parser.rb
-  revision: 54b17ba8c7d8d20a16dfc65d1775241833219cf2
-  ref: 54b17ba8c7d8d20a16dfc65d1775241833219cf2
-  submodules: true
-  specs:
-    http_parser.rb (0.6.1)
-
 GIT
   remote: https://github.com/witgo/nilsimsa
   revision: fd184883048b922b176939f851338d0a4971a532
@@ -709,7 +701,6 @@ DEPENDENCIES
   htmlentities (~> 4.3)
   http (~> 4.4)
   http_accept_language (~> 2.1)
-  http_parser.rb (~> 0.6)!
   httplog (~> 1.4.3)
   i18n-tasks (~> 0.9)
   idn-ruby
diff --git a/app/controllers/accounts_controller.rb b/app/controllers/accounts_controller.rb
index f5e82692e..b42f711f0 100644
--- a/app/controllers/accounts_controller.rb
+++ b/app/controllers/accounts_controller.rb
@@ -82,7 +82,7 @@ class AccountsController < ApplicationController
   end
 
   def account_media_status_ids
-    @account.media_attachments.attached.reorder(nil).select(:status_id).distinct
+    @account.media_attachments.attached.reorder(nil).select(:status_id).group(:status_id)
   end
 
   def no_replies_scope
diff --git a/app/controllers/admin/statuses_controller.rb b/app/controllers/admin/statuses_controller.rb
index 650195034..d7c192f0d 100644
--- a/app/controllers/admin/statuses_controller.rb
+++ b/app/controllers/admin/statuses_controller.rb
@@ -14,7 +14,7 @@ module Admin
       @statuses = @account.statuses.where(visibility: [:public, :unlisted])
 
       if params[:media]
-        account_media_status_ids = @account.media_attachments.attached.reorder(nil).select(:status_id).distinct
+        account_media_status_ids = @account.media_attachments.attached.reorder(nil).select(:status_id).group(:status_id)
         @statuses.merge!(Status.where(id: account_media_status_ids))
       end
 
diff --git a/app/controllers/api/base_controller.rb b/app/controllers/api/base_controller.rb
index 045e7dd26..055cd416d 100644
--- a/app/controllers/api/base_controller.rb
+++ b/app/controllers/api/base_controller.rb
@@ -102,7 +102,7 @@ class Api::BaseController < ApplicationController
     elsif !current_user.approved?
       render json: { error: 'Your login is currently pending approval' }, status: 403
     else
-      set_user_activity
+      update_user_sign_in
     end
   end
 
diff --git a/app/controllers/auth/sessions_controller.rb b/app/controllers/auth/sessions_controller.rb
index 1fd755334..783338450 100644
--- a/app/controllers/auth/sessions_controller.rb
+++ b/app/controllers/auth/sessions_controller.rb
@@ -7,6 +7,7 @@ class Auth::SessionsController < Devise::SessionsController
 
   skip_before_action :require_no_authentication, only: [:create]
   skip_before_action :require_functional!
+  skip_before_action :update_user_sign_in
 
   include TwoFactorAuthenticationConcern
   include SignInTokenAuthenticationConcern
@@ -24,6 +25,7 @@ class Auth::SessionsController < Devise::SessionsController
 
   def create
     super do |resource|
+      resource.update_sign_in!(request, new_sign_in: true)
       remember_me(resource)
       flash.delete(:notice)
     end
@@ -41,7 +43,7 @@ class Auth::SessionsController < Devise::SessionsController
 
   def find_user
     if session[:attempt_user_id]
-      User.find(session[:attempt_user_id])
+      User.find_by(id: session[:attempt_user_id])
     else
       user   = User.authenticate_with_ldap(user_params) if Devise.ldap_authentication
       user ||= User.authenticate_with_pam(user_params) if Devise.pam_authentication
@@ -74,6 +76,7 @@ class Auth::SessionsController < Devise::SessionsController
 
   def require_no_authentication
     super
+
     # Delete flash message that isn't entirely useful and may be confusing in
     # most cases because /web doesn't display/clear flash messages.
     flash.delete(:alert) if flash[:alert] == I18n.t('devise.failure.already_authenticated')
@@ -91,13 +94,30 @@ class Auth::SessionsController < Devise::SessionsController
 
   def home_paths(resource)
     paths = [about_path]
+
     if single_user_mode? && resource.is_a?(User)
       paths << short_account_path(username: resource.account)
     end
+
     paths
   end
 
   def continue_after?
     truthy_param?(:continue)
   end
+
+  def restart_session
+    clear_attempt_from_session
+    redirect_to new_user_session_path, alert: I18n.t('devise.failure.timeout')
+  end
+
+  def set_attempt_session(user)
+    session[:attempt_user_id]         = user.id
+    session[:attempt_user_updated_at] = user.updated_at.to_s
+  end
+
+  def clear_attempt_from_session
+    session.delete(:attempt_user_id)
+    session.delete(:attempt_user_updated_at)
+  end
 end
diff --git a/app/controllers/concerns/sign_in_token_authentication_concern.rb b/app/controllers/concerns/sign_in_token_authentication_concern.rb
index 91f813acc..3c95a4afd 100644
--- a/app/controllers/concerns/sign_in_token_authentication_concern.rb
+++ b/app/controllers/concerns/sign_in_token_authentication_concern.rb
@@ -18,7 +18,9 @@ module SignInTokenAuthenticationConcern
   def authenticate_with_sign_in_token
     user = self.resource = find_user
 
-    if user_params[:sign_in_token_attempt].present? && session[:attempt_user_id]
+    if user.present? && session[:attempt_user_id].present? && session[:attempt_user_updated_at] != user.updated_at.to_s
+      restart_session
+    elsif user_params.key?(:sign_in_token_attempt) && session[:attempt_user_id]
       authenticate_with_sign_in_token_attempt(user)
     elsif user.present? && user.external_or_valid_password?(user_params[:password])
       prompt_for_sign_in_token(user)
@@ -27,7 +29,7 @@ module SignInTokenAuthenticationConcern
 
   def authenticate_with_sign_in_token_attempt(user)
     if valid_sign_in_token_attempt?(user)
-      session.delete(:attempt_user_id)
+      clear_attempt_from_session
       remember_me(user)
       sign_in(user)
     else
@@ -42,10 +44,10 @@ module SignInTokenAuthenticationConcern
       UserMailer.sign_in_token(user, request.remote_ip, request.user_agent, Time.now.utc.to_s).deliver_later!
     end
 
-    set_locale do
-      session[:attempt_user_id] = user.id
-      @body_classes = 'lighter'
-      render :sign_in_token
-    end
+    set_attempt_session(user)
+
+    @body_classes = 'lighter'
+
+    set_locale { render :sign_in_token }
   end
 end
diff --git a/app/controllers/concerns/two_factor_authentication_concern.rb b/app/controllers/concerns/two_factor_authentication_concern.rb
index daafe56f4..f54a3c829 100644
--- a/app/controllers/concerns/two_factor_authentication_concern.rb
+++ b/app/controllers/concerns/two_factor_authentication_concern.rb
@@ -21,7 +21,9 @@ module TwoFactorAuthenticationConcern
   def authenticate_with_two_factor
     user = self.resource = find_user
 
-    if user_params[:otp_attempt].present? && session[:attempt_user_id]
+    if user.present? && session[:attempt_user_id].present? && session[:attempt_user_updated_at] != user.updated_at.to_s
+      restart_session
+    elsif user_params[:otp_attempt].present? && session[:attempt_user_id]
       authenticate_with_two_factor_attempt(user)
     elsif user.present? && user.external_or_valid_password?(user_params[:password])
       prompt_for_two_factor(user)
@@ -30,7 +32,7 @@ module TwoFactorAuthenticationConcern
 
   def authenticate_with_two_factor_attempt(user)
     if valid_otp_attempt?(user)
-      session.delete(:attempt_user_id)
+      clear_attempt_from_session
       remember_me(user)
       sign_in(user)
     else
@@ -40,10 +42,10 @@ module TwoFactorAuthenticationConcern
   end
 
   def prompt_for_two_factor(user)
-    set_locale do
-      session[:attempt_user_id] = user.id
-      @body_classes = 'lighter'
-      render :two_factor
-    end
+    set_attempt_session(user)
+
+    @body_classes = 'lighter'
+
+    set_locale { render :two_factor }
   end
 end
diff --git a/app/controllers/concerns/user_tracking_concern.rb b/app/controllers/concerns/user_tracking_concern.rb
index be10705fc..efda37fae 100644
--- a/app/controllers/concerns/user_tracking_concern.rb
+++ b/app/controllers/concerns/user_tracking_concern.rb
@@ -6,14 +6,13 @@ module UserTrackingConcern
   UPDATE_SIGN_IN_HOURS = 24
 
   included do
-    before_action :set_user_activity
+    before_action :update_user_sign_in
   end
 
   private
 
-  def set_user_activity
-    return unless user_needs_sign_in_update?
-    current_user.update_tracked_fields!(request)
+  def update_user_sign_in
+    current_user.update_sign_in!(request) if user_needs_sign_in_update?
   end
 
   def user_needs_sign_in_update?
diff --git a/app/lib/activitypub/activity/move.rb b/app/lib/activitypub/activity/move.rb
index 2103f503f..7e073f64d 100644
--- a/app/lib/activitypub/activity/move.rb
+++ b/app/lib/activitypub/activity/move.rb
@@ -20,6 +20,9 @@ class ActivityPub::Activity::Move < ActivityPub::Activity
 
     # Initiate a re-follow for each follower
     MoveWorker.perform_async(origin_account.id, target_account.id)
+  rescue
+    unmark_as_processing!
+    raise
   end
 
   private
diff --git a/app/models/account.rb b/app/models/account.rb
index 6b7ebda9e..9288c7fe8 100644
--- a/app/models/account.rb
+++ b/app/models/account.rb
@@ -415,7 +415,7 @@ class Account < ApplicationRecord
     end
 
     def inboxes
-      urls = reorder(nil).where(protocol: :activitypub).pluck(Arel.sql("distinct coalesce(nullif(accounts.shared_inbox_url, ''), accounts.inbox_url)"))
+      urls = reorder(nil).where(protocol: :activitypub).group(:preferred_inbox_url).pluck(Arel.sql("coalesce(nullif(accounts.shared_inbox_url, ''), accounts.inbox_url) AS preferred_inbox_url"))
       DeliveryFailureTracker.without_unavailable(urls)
     end
 
diff --git a/app/models/account_stat.rb b/app/models/account_stat.rb
index c84e4217c..e70b54d79 100644
--- a/app/models/account_stat.rb
+++ b/app/models/account_stat.rb
@@ -21,26 +21,26 @@ class AccountStat < ApplicationRecord
 
   def increment_count!(key)
     update(attributes_for_increment(key))
-  rescue ActiveRecord::StaleObjectError
+  rescue ActiveRecord::StaleObjectError, ActiveRecord::RecordNotUnique
     begin
       reload_with_id
     rescue ActiveRecord::RecordNotFound
-      # Nothing to do
-    else
-      retry
+      return
     end
+
+    retry
   end
 
   def decrement_count!(key)
-    update(key => [public_send(key) - 1, 0].max)
-  rescue ActiveRecord::StaleObjectError
+    update(attributes_for_decrement(key))
+  rescue ActiveRecord::StaleObjectError, ActiveRecord::RecordNotUnique
     begin
       reload_with_id
     rescue ActiveRecord::RecordNotFound
-      # Nothing to do
-    else
-      retry
+      return
     end
+
+    retry
   end
 
   private
@@ -51,8 +51,13 @@ class AccountStat < ApplicationRecord
     attrs
   end
 
+  def attributes_for_decrement(key)
+    attrs = { key => [public_send(key) - 1, 0].max }
+    attrs
+  end
+
   def reload_with_id
-    self.id = find_by!(account: account).id if new_record?
+    self.id = self.class.find_by!(account: account).id if new_record?
     reload
   end
 end
diff --git a/app/models/form/account_batch.rb b/app/models/form/account_batch.rb
index 0b285fde9..fc6ab5c90 100644
--- a/app/models/form/account_batch.rb
+++ b/app/models/form/account_batch.rb
@@ -43,7 +43,7 @@ class Form::AccountBatch
   end
 
   def account_domains
-    accounts.pluck(Arel.sql('distinct domain')).compact
+    accounts.group(:domain).pluck(:domain).compact
   end
 
   def accounts
diff --git a/app/models/tag.rb b/app/models/tag.rb
index bce76fc16..0870afc41 100644
--- a/app/models/tag.rb
+++ b/app/models/tag.rb
@@ -126,7 +126,7 @@ class Tag < ApplicationRecord
     end
 
     def search_for(term, limit = 5, offset = 0, options = {})
-      normalized_term = normalize(term.strip).mb_chars.downcase.to_s
+      normalized_term = normalize(term.strip)
       pattern         = sanitize_sql_like(normalized_term) + '%'
       query           = Tag.listable.where(arel_table[:name].lower.matches(pattern))
       query           = query.where(arel_table[:name].lower.eq(normalized_term).or(arel_table[:reviewed_at].not_eq(nil))) if options[:exclude_unreviewed]
diff --git a/app/models/user.rb b/app/models/user.rb
index 306e2d435..0efeed9f7 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -61,7 +61,7 @@ class User < ApplicationRecord
   devise :two_factor_backupable,
          otp_number_of_backup_codes: 10
 
-  devise :registerable, :recoverable, :rememberable, :trackable, :validatable,
+  devise :registerable, :recoverable, :rememberable, :validatable,
          :confirmable
 
   include Omniauthable
@@ -161,6 +161,24 @@ class User < ApplicationRecord
     prepare_new_user! if new_user && approved?
   end
 
+  def update_sign_in!(request, new_sign_in: false)
+    old_current, new_current = current_sign_in_at, Time.now.utc
+    self.last_sign_in_at     = old_current || new_current
+    self.current_sign_in_at  = new_current
+
+    old_current, new_current = current_sign_in_ip, request.remote_ip
+    self.last_sign_in_ip     = old_current || new_current
+    self.current_sign_in_ip  = new_current
+
+    if new_sign_in
+      self.sign_in_count ||= 0
+      self.sign_in_count  += 1
+    end
+
+    save(validate: false) unless new_record?
+    prepare_returning_user!
+  end
+
   def pending?
     !approved?
   end
@@ -192,11 +210,6 @@ class User < ApplicationRecord
     prepare_new_user!
   end
 
-  def update_tracked_fields!(request)
-    super
-    prepare_returning_user!
-  end
-
   def disable_two_factor!
     self.otp_required_for_login = false
     otp_backup_codes&.clear
diff --git a/app/services/activitypub/process_account_service.rb b/app/services/activitypub/process_account_service.rb
index 23dc9c3e7..eb14bbbe8 100644
--- a/app/services/activitypub/process_account_service.rb
+++ b/app/services/activitypub/process_account_service.rb
@@ -198,7 +198,7 @@ class ActivityPub::ProcessAccountService < BaseService
     total_items = collection.is_a?(Hash) && collection['totalItems'].present? && collection['totalItems'].is_a?(Numeric) ? collection['totalItems'] : nil
     has_first_page = collection.is_a?(Hash) && collection['first'].present?
     @collections[type] = [total_items, has_first_page]
-  rescue HTTP::Error, OpenSSL::SSL::SSLError
+  rescue HTTP::Error, OpenSSL::SSL::SSLError, Mastodon::LengthValidationError
     @collections[type] = [nil, nil]
   end
 
diff --git a/app/services/resolve_account_service.rb b/app/services/resolve_account_service.rb
index 3f7bb7cc5..f8d61611f 100644
--- a/app/services/resolve_account_service.rb
+++ b/app/services/resolve_account_service.rb
@@ -31,6 +31,7 @@ class ResolveAccountService < BaseService
     # At this point we are in need of a Webfinger query, which may
     # yield us a different username/domain through a redirect
     process_webfinger!(@uri)
+    @domain = nil if TagManager.instance.local_domain?(@domain)
 
     # Because the username/domain pair may be different than what
     # we already checked, we need to check if we've already got
@@ -45,7 +46,7 @@ class ResolveAccountService < BaseService
     # Now it is certain, it is definitely a remote account, and it
     # either needs to be created, or updated from fresh data
 
-    process_account!
+    fetch_account!
   rescue Webfinger::Error, WebfingerRedirectError, Oj::ParseError => e
     Rails.logger.debug "Webfinger query for #{@uri} failed: #{e}"
     nil
@@ -75,33 +76,35 @@ class ResolveAccountService < BaseService
     @uri = [@username, @domain].compact.join('@')
   end
 
-  def process_webfinger!(uri, redirected = false)
+  def process_webfinger!(uri)
     @webfinger                           = webfinger!("acct:#{uri}")
-    confirmed_username, confirmed_domain = @webfinger.subject.gsub(/\Aacct:/, '').split('@')
+    confirmed_username, confirmed_domain = split_acct(@webfinger.subject)
 
     if confirmed_username.casecmp(@username).zero? && confirmed_domain.casecmp(@domain).zero?
       @username = confirmed_username
       @domain   = confirmed_domain
-      @uri      = uri
-    elsif !redirected
-      return process_webfinger!("#{confirmed_username}@#{confirmed_domain}", true)
-    else
-      raise WebfingerRedirectError, "The URI #{uri} tries to hijack #{@username}@#{@domain}"
+      return
     end
 
-    @domain = nil if TagManager.instance.local_domain?(@domain)
+    # Account doesn't match, so it may have been redirected
+    @webfinger         = webfinger!("acct:#{confirmed_username}@#{confirmed_domain}")
+    @username, @domain = split_acct(@webfinger.subject)
+
+    unless confirmed_username.casecmp(@username).zero? && confirmed_domain.casecmp(@domain).zero?
+      raise WebfingerRedirectError, "The URI #{uri} tries to hijack #{@username}@#{@domain}"
+    end
   end
 
-  def process_account!
+  def split_acct(acct)
+    acct.gsub(/\Aacct:/, '').split('@')
+  end
+
+  def fetch_account!
     return unless activitypub_ready?
 
     RedisLock.acquire(lock_options) do |lock|
       if lock.acquired?
-        @account = Account.find_remote(@username, @domain)
-
-        next if actor_json.nil?
-
-        @account = ActivityPub::ProcessAccountService.new.call(@username, @domain, actor_json)
+        @account = ActivityPub::FetchRemoteAccountService.new.call(actor_url)
       else
         raise Mastodon::RaceConditionError
       end
diff --git a/chart/Chart.yaml b/chart/Chart.yaml
index 783569451..4144ba8b1 100644
--- a/chart/Chart.yaml
+++ b/chart/Chart.yaml
@@ -15,12 +15,12 @@ type: application
 # This is the chart version. This version number should be incremented each time you make changes
 # to the chart and its templates, including the app version.
 # Versions are expected to follow Semantic Versioning (https://semver.org/)
-version: 0.1.0
+version: 0.1.1
 
 # This is the version number of the application being deployed. This version number should be
 # incremented each time you make changes to the application. Versions are not expected to
 # follow Semantic Versioning. They should reflect the version the application is using.
-appVersion: 3.1.5
+appVersion: 3.2.2
 
 dependencies:
   - name: elasticsearch
diff --git a/chart/values.yaml.template b/chart/values.yaml.template
index 694bc4d42..e1984068c 100644
--- a/chart/values.yaml.template
+++ b/chart/values.yaml.template
@@ -4,7 +4,7 @@ image:
   repository: tootsuite/mastodon
   pullPolicy: Always
   # https://hub.docker.com/r/tootsuite/mastodon/tags
-  tag: v3.1.5
+  tag: v3.2.2
   # alternatively, use `latest` for the latest release or `edge` for the image
   # built from the most recent commit
   #
diff --git a/db/migrate/20200620164023_add_fixed_lowercase_index_to_accounts.rb b/db/migrate/20200620164023_add_fixed_lowercase_index_to_accounts.rb
index c5688681f..c3aa8e33c 100644
--- a/db/migrate/20200620164023_add_fixed_lowercase_index_to_accounts.rb
+++ b/db/migrate/20200620164023_add_fixed_lowercase_index_to_accounts.rb
@@ -1,10 +1,30 @@
 class AddFixedLowercaseIndexToAccounts < ActiveRecord::Migration[5.2]
   disable_ddl_transaction!
 
+  class CorruptionError < StandardError
+    def cause
+      nil
+    end
+
+    def backtrace
+      []
+    end
+  end
+
   def up
-    rename_index :accounts, 'index_accounts_on_username_and_domain_lower', 'old_index_accounts_on_username_and_domain_lower' unless index_name_exists?(:accounts, 'old_index_accounts_on_username_and_domain_lower')
-    add_index :accounts, "lower (username), COALESCE(lower(domain), '')", name: 'index_accounts_on_username_and_domain_lower', unique: true, algorithm: :concurrently
-    remove_index :accounts, name: 'old_index_accounts_on_username_and_domain_lower'
+    if index_name_exists?(:accounts, 'old_index_accounts_on_username_and_domain_lower') && index_name_exists?(:accounts, 'index_accounts_on_username_and_domain_lower')
+      remove_index :accounts, name: 'index_accounts_on_username_and_domain_lower'
+    elsif index_name_exists?(:accounts, 'index_accounts_on_username_and_domain_lower')
+      rename_index :accounts, 'index_accounts_on_username_and_domain_lower', 'old_index_accounts_on_username_and_domain_lower'
+    end
+
+    begin
+      add_index :accounts, "lower (username), COALESCE(lower(domain), '')", name: 'index_accounts_on_username_and_domain_lower', unique: true, algorithm: :concurrently
+    rescue ActiveRecord::RecordNotUnique
+      raise CorruptionError, 'Migration failed because of index corruption, see https://docs.joinmastodon.org/admin/troubleshooting/index-corruption/#fixing'
+    end
+
+    remove_index :accounts, name: 'old_index_accounts_on_username_and_domain_lower' if index_name_exists?(:accounts, 'old_index_accounts_on_username_and_domain_lower')
   end
 
   def down
diff --git a/lib/cli.rb b/lib/cli.rb
index 9162144cc..38df8abcc 100644
--- a/lib/cli.rb
+++ b/lib/cli.rb
@@ -13,6 +13,7 @@ require_relative 'mastodon/preview_cards_cli'
 require_relative 'mastodon/cache_cli'
 require_relative 'mastodon/upgrade_cli'
 require_relative 'mastodon/email_domain_blocks_cli'
+require_relative 'mastodon/maintenance_cli'
 require_relative 'mastodon/version'
 
 module Mastodon
@@ -57,6 +58,9 @@ module Mastodon
     desc 'email_domain_blocks SUBCOMMAND ...ARGS', 'Manage e-mail domain blocks'
     subcommand 'email_domain_blocks', Mastodon::EmailDomainBlocksCLI
 
+    desc 'maintenance SUBCOMMAND ...ARGS', 'Various maintenance utilities'
+    subcommand 'maintenance', Mastodon::MaintenanceCLI
+
     option :dry_run, type: :boolean
     desc 'self-destruct', 'Erase the server from the federation'
     long_desc <<~LONG_DESC
diff --git a/lib/mastodon/maintenance_cli.rb b/lib/mastodon/maintenance_cli.rb
new file mode 100644
index 000000000..822051ceb
--- /dev/null
+++ b/lib/mastodon/maintenance_cli.rb
@@ -0,0 +1,618 @@
+# frozen_string_literal: true
+
+require 'tty-prompt'
+require_relative '../../config/boot'
+require_relative '../../config/environment'
+require_relative 'cli_helper'
+
+module Mastodon
+  class MaintenanceCLI < Thor
+    include CLIHelper
+
+    def self.exit_on_failure?
+      true
+    end
+
+    MIN_SUPPORTED_VERSION = 2019_10_01_213028
+    MAX_SUPPORTED_VERSION = 2020_12_18_054746
+
+    # Stubs to enjoy ActiveRecord queries while not depending on a particular
+    # version of the code/database
+
+    class Status < ApplicationRecord; end
+    class StatusPin < ApplicationRecord; end
+    class Poll < ApplicationRecord; end
+    class Report < ApplicationRecord; end
+    class Tombstone < ApplicationRecord; end
+    class Favourite < ApplicationRecord; end
+    class Follow < ApplicationRecord; end
+    class FollowRequest < ApplicationRecord; end
+    class Block < ApplicationRecord; end
+    class Mute < ApplicationRecord; end
+    class AccountIdentityProof < ApplicationRecord; end
+    class AccountModerationNote < ApplicationRecord; end
+    class AccountPin < ApplicationRecord; end
+    class ListAccount < ApplicationRecord; end
+    class PollVote < ApplicationRecord; end
+    class Mention < ApplicationRecord; end
+    class AccountDomainBlock < ApplicationRecord; end
+    class AnnouncementReaction < ApplicationRecord; end
+    class FeaturedTag < ApplicationRecord; end
+    class CustomEmoji < ApplicationRecord; end
+    class CustomEmojiCategory < ApplicationRecord; end
+    class Bookmark < ApplicationRecord; end
+    class WebauthnCredential < ApplicationRecord; end
+
+    class PreviewCard < ApplicationRecord
+      self.inheritance_column = false
+    end
+
+    class MediaAttachment < ApplicationRecord
+      self.inheritance_column = nil
+    end
+
+    class AccountStat < ApplicationRecord
+      belongs_to :account, inverse_of: :account_stat
+    end
+
+    # Dummy class, to make migration possible across version changes
+    class Account < ApplicationRecord
+      has_one :user, inverse_of: :account
+      has_one :account_stat, inverse_of: :account
+
+      scope :local, -> { where(domain: nil) }
+
+      def local?
+        domain.nil?
+      end
+
+      def acct
+        local? ? username : "#{username}@#{domain}"
+      end
+
+      # This is a duplicate of the AccountMerging concern because we need it to
+      # be independent from code version.
+      def merge_with!(other_account)
+        # Since it's the same remote resource, the remote resource likely
+        # already believes we are following/blocking, so it's safe to
+        # re-attribute the relationships too. However, during the presence
+        # of the index bug users could have *also* followed the reference
+        # account already, therefore mass update will not work and we need
+        # to check for (and skip past) uniqueness errors
+
+        owned_classes = [
+          Status, StatusPin, MediaAttachment, Poll, Report, Tombstone, Favourite,
+          Follow, FollowRequest, Block, Mute, AccountIdentityProof,
+          AccountModerationNote, AccountPin, AccountStat, ListAccount,
+          PollVote, Mention
+        ]
+        owned_classes << AccountDeletionRequest if ActiveRecord::Base.connection.table_exists?(:account_deletion_requests)
+        owned_classes << AccountNote if ActiveRecord::Base.connection.table_exists?(:account_notes)
+
+        owned_classes.each do |klass|
+          klass.where(account_id: other_account.id).find_each do |record|
+            begin
+              record.update_attribute(:account_id, id)
+            rescue ActiveRecord::RecordNotUnique
+              next
+            end
+          end
+        end
+
+        target_classes = [Follow, FollowRequest, Block, Mute, AccountModerationNote, AccountPin]
+        target_classes << AccountNote if ActiveRecord::Base.connection.table_exists?(:account_notes)
+
+        target_classes.each do |klass|
+          klass.where(target_account_id: other_account.id).find_each do |record|
+            begin
+              record.update_attribute(:target_account_id, id)
+            rescue ActiveRecord::RecordNotUnique
+              next
+            end
+          end
+        end
+      end
+    end
+
+    class User < ApplicationRecord
+      belongs_to :account, inverse_of: :user
+    end
+
+    desc 'fix-duplicates', 'Fix duplicates in database and rebuild indexes'
+    long_desc <<~LONG_DESC
+      Delete or merge duplicate accounts, statuses, emojis, etc. and rebuild indexes.
+
+      This is useful if your database indexes are corrupted because of issues such as https://wiki.postgresql.org/wiki/Locale_data_changes
+
+      Mastodon has to be stopped to run this task, which will take a long time and may be destructive.
+    LONG_DESC
+    def fix_duplicates
+      @prompt = TTY::Prompt.new
+
+      if ActiveRecord::Migrator.current_version < MIN_SUPPORTED_VERSION
+        @prompt.warn 'Your version of the database schema is too old and is not supported by this script.'
+        @prompt.warn 'Please update to at least Mastodon 3.0.0 before running this script.'
+        exit(1)
+      elsif ActiveRecord::Migrator.current_version > MAX_SUPPORTED_VERSION
+        @prompt.warn 'Your version of the database schema is more recent than this script, this may cause unexpected errors.'
+        exit(1) unless @prompt.yes?('Continue anyway?')
+      end
+
+      @prompt.warn 'This task will take a long time to run and is potentially destructive.'
+      @prompt.warn 'Please make sure to stop Mastodon and have a backup.'
+      exit(1) unless @prompt.yes?('Continue?')
+
+      deduplicate_accounts!
+      deduplicate_users!
+      deduplicate_account_domain_blocks!
+      deduplicate_account_identity_proofs!
+      deduplicate_announcement_reactions!
+      deduplicate_conversations!
+      deduplicate_custom_emojis!
+      deduplicate_custom_emoji_categories!
+      deduplicate_domain_allows!
+      deduplicate_domain_blocks!
+      deduplicate_unavailable_domains!
+      deduplicate_email_domain_blocks!
+      deduplicate_media_attachments!
+      deduplicate_preview_cards!
+      deduplicate_statuses!
+      deduplicate_tags!
+      deduplicate_webauthn_credentials!
+
+      Rails.cache.clear
+
+      @prompt.say 'Finished!'
+    end
+
+    private
+
+    def deduplicate_accounts!
+      remove_index_if_exists!(:accounts, 'index_accounts_on_username_and_domain_lower')
+
+      @prompt.say 'Deduplicating accounts… for local accounts, you will be asked to chose which account to keep unchanged.'
+
+      find_duplicate_accounts.each do |row|
+        accounts = Account.where(id: row['ids'].split(',')).to_a
+
+        if accounts.first.local?
+          deduplicate_local_accounts!(accounts)
+        else
+          deduplicate_remote_accounts!(accounts)
+        end
+      end
+
+      @prompt.say 'Restoring index_accounts_on_username_and_domain_lower…'
+      if ActiveRecord::Migrator.current_version < 20200620164023
+        ActiveRecord::Base.connection.add_index :accounts, 'lower (username), lower(domain)', name: 'index_accounts_on_username_and_domain_lower', unique: true
+      else
+        ActiveRecord::Base.connection.add_index :accounts, "lower (username), COALESCE(lower(domain), '')", name: 'index_accounts_on_username_and_domain_lower', unique: true
+      end
+    end
+
+    def deduplicate_users!
+      remove_index_if_exists!(:users, 'index_users_on_confirmation_token')
+      remove_index_if_exists!(:users, 'index_users_on_email')
+      remove_index_if_exists!(:users, 'index_users_on_remember_token')
+      remove_index_if_exists!(:users, 'index_users_on_reset_password_token')
+
+      @prompt.say 'Deduplicating user records…'
+
+      # Deduplicating email
+      ActiveRecord::Base.connection.select_all("SELECT string_agg(id::text, ',') AS ids FROM users GROUP BY email HAVING count(*) > 1").each do |row|
+        users = User.where(id: row['ids'].split(',')).sort_by(&:updated_at).reverse
+        ref_user = users.shift
+        @prompt.warn "Multiple users registered with e-mail address #{ref_user.email}."
+        @prompt.warn "e-mail will be disabled for the following accounts: #{user.map(&:account).map(&:acct).join(', ')}"
+        @prompt.warn 'Please reach out to them and set another address with `tootctl account modify` or delete them.'
+
+        i = 0
+        users.each do |user|
+          user.update!(email: "#{i} " + user.email)
+        end
+      end
+
+      ActiveRecord::Base.connection.select_all("SELECT string_agg(id::text, ',') AS ids FROM users WHERE confirmation_token IS NOT NULL GROUP BY confirmation_token HAVING count(*) > 1").each do |row|
+        users = User.where(id: row['ids'].split(',')).sort_by(&:created_at).reverse.drop(1)
+        @prompt.warn "Unsetting confirmation token for those accounts: #{users.map(&:account).map(&:acct).join(', ')}"
+
+        users.each do |user|
+          user.update!(confirmation_token: nil)
+        end
+      end
+
+      ActiveRecord::Base.connection.select_all("SELECT string_agg(id::text, ',') AS ids FROM users WHERE remember_token IS NOT NULL GROUP BY remember_token HAVING count(*) > 1").each do |row|
+        users = User.where(id: row['ids'].split(',')).sort_by(&:updated_at).reverse.drop(1)
+        @prompt.warn "Unsetting remember token for those accounts: #{users.map(&:account).map(&:acct).join(', ')}"
+
+        users.each do |user|
+          user.update!(remember_token: nil)
+        end
+      end
+
+      ActiveRecord::Base.connection.select_all("SELECT string_agg(id::text, ',') AS ids FROM users WHERE reset_password_token IS NOT NULL GROUP BY reset_password_token HAVING count(*) > 1").each do |row|
+        users = User.where(id: row['ids'].split(',')).sort_by(&:updated_at).reverse.drop(1)
+        @prompt.warn "Unsetting password reset token for those accounts: #{users.map(&:account).map(&:acct).join(', ')}"
+
+        users.each do |user|
+          user.update!(reset_password_token: nil)
+        end
+      end
+
+      @prompt.say 'Restoring users indexes…'
+      ActiveRecord::Base.connection.add_index :users, ['confirmation_token'], name: 'index_users_on_confirmation_token', unique: true
+      ActiveRecord::Base.connection.add_index :users, ['email'], name: 'index_users_on_email', unique: true
+      ActiveRecord::Base.connection.add_index :users, ['remember_token'], name: 'index_users_on_remember_token', unique: true
+      ActiveRecord::Base.connection.add_index :users, ['reset_password_token'], name: 'index_users_on_reset_password_token', unique: true
+    end
+
+    def deduplicate_account_domain_blocks!
+      remove_index_if_exists!(:account_domain_blocks, 'index_account_domain_blocks_on_account_id_and_domain')
+
+      @prompt.say 'Removing duplicate account domain blocks…'
+      ActiveRecord::Base.connection.select_all("SELECT string_agg(id::text, ',') AS ids FROM account_domain_blocks GROUP BY account_id, domain HAVING count(*) > 1").each do |row|
+        AccountDomainBlock.where(id: row['ids'].split(',').drop(1)).delete_all
+      end
+
+      @prompt.say 'Restoring account domain blocks indexes…'
+      ActiveRecord::Base.connection.add_index :account_domain_blocks, ['account_id', 'domain'], name: 'index_account_domain_blocks_on_account_id_and_domain', unique: true
+    end
+
+    def deduplicate_account_identity_proofs!
+      remove_index_if_exists!(:account_identity_proofs, 'index_account_proofs_on_account_and_provider_and_username')
+
+      @prompt.say 'Removing duplicate account identity proofs…'
+      ActiveRecord::Base.connection.select_all("SELECT string_agg(id::text, ',') AS ids FROM account_identity_proofs GROUP BY account_id, provider, provider_username HAVING count(*) > 1").each do |row|
+        AccountIdentityProof.where(id: row['ids'].split(',')).sort_by(&:id).reverse.drop(1).each(&:destroy)
+      end
+
+      @prompt.say 'Restoring account identity proofs indexes…'
+      ActiveRecord::Base.connection.add_index :account_identity_proofs, ['account_id', 'provider', 'provider_username'], name: 'index_account_proofs_on_account_and_provider_and_username', unique: true
+    end
+
+    def deduplicate_announcement_reactions!
+      return unless ActiveRecord::Base.connection.table_exists?(:announcement_reactions)
+
+      remove_index_if_exists!(:announcement_reactions, 'index_announcement_reactions_on_account_id_and_announcement_id')
+
+      @prompt.say 'Removing duplicate account identity proofs…'
+      ActiveRecord::Base.connection.select_all("SELECT string_agg(id::text, ',') AS ids FROM announcement_reactions GROUP BY account_id, announcement_id, name HAVING count(*) > 1").each do |row|
+        AnnouncementReaction.where(id: row['ids'].split(',')).sort_by(&:id).reverse.drop(1).each(&:destroy)
+      end
+
+      @prompt.say 'Restoring announcement_reactions indexes…'
+      ActiveRecord::Base.connection.add_index :announcement_reactions, ['account_id', 'announcement_id', 'name'], name: 'index_announcement_reactions_on_account_id_and_announcement_id', unique: true
+    end
+
+    def deduplicate_conversations!
+      remove_index_if_exists!(:conversations, 'index_conversations_on_uri')
+
+      @prompt.say 'Deduplicating conversations…'
+      ActiveRecord::Base.connection.select_all("SELECT string_agg(id::text, ',') AS ids FROM conversations WHERE uri IS NOT NULL GROUP BY uri HAVING count(*) > 1").each do |row|
+        conversations = Conversation.where(id: row['ids'].split(',')).sort_by(&:id).reverse
+
+        ref_conversation = conversations.shift
+
+        conversations.each do |other|
+          merge_conversations!(ref_conversation, other)
+          other.destroy
+        end
+      end
+
+      @prompt.say 'Restoring conversations indexes…'
+      ActiveRecord::Base.connection.add_index :conversations, ['uri'], name: 'index_conversations_on_uri', unique: true
+    end
+
+    def deduplicate_custom_emojis!
+      remove_index_if_exists!(:custom_emojis, 'index_custom_emojis_on_shortcode_and_domain')
+
+      @prompt.say 'Deduplicating custom_emojis…'
+      ActiveRecord::Base.connection.select_all("SELECT string_agg(id::text, ',') AS ids FROM custom_emojis GROUP BY shortcode, domain HAVING count(*) > 1").each do |row|
+        emojis = CustomEmoji.where(id: row['ids'].split(',')).sort_by(&:id).reverse
+
+        ref_emoji = emojis.shift
+
+        emojis.each do |other|
+          merge_custom_emojis!(ref_emoji, other)
+          other.destroy
+        end
+      end
+
+      @prompt.say 'Restoring custom_emojis indexes…'
+      ActiveRecord::Base.connection.add_index :custom_emojis, ['shortcode', 'domain'], name: 'index_custom_emojis_on_shortcode_and_domain', unique: true
+    end
+
+    def deduplicate_custom_emoji_categories!
+      remove_index_if_exists!(:custom_emoji_categories, 'index_custom_emoji_categories_on_name')
+
+      @prompt.say 'Deduplicating custom_emoji_categories…'
+      ActiveRecord::Base.connection.select_all("SELECT string_agg(id::text, ',') AS ids FROM custom_emoji_categories GROUP BY name HAVING count(*) > 1").each do |row|
+        categories = CustomEmojiCategory.where(id: row['ids'].split(',')).sort_by(&:id).reverse
+
+        ref_category = categories.shift
+
+        categories.each do |other|
+          merge_custom_emoji_categories!(ref_category, other)
+          other.destroy
+        end
+      end
+
+      @prompt.say 'Restoring custom_emoji_categories indexes…'
+      ActiveRecord::Base.connection.add_index :custom_emoji_categories, ['name'], name: 'index_custom_emoji_categories_on_name', unique: true
+    end
+
+    def deduplicate_domain_allows!
+      remove_index_if_exists!(:domain_allows, 'index_domain_allows_on_domain')
+
+      @prompt.say 'Deduplicating domain_allows…'
+      ActiveRecord::Base.connection.select_all("SELECT string_agg(id::text, ',') AS ids FROM domain_allows GROUP BY domain HAVING count(*) > 1").each do |row|
+        DomainAllow.where(id: row['ids'].split(',')).sort_by(&:id).reverse.drop(1).each(&:destroy)
+      end
+
+      @prompt.say 'Restoring domain_allows indexes…'
+      ActiveRecord::Base.connection.add_index :domain_allows, ['domain'], name: 'index_domain_allows_on_domain', unique: true
+    end
+
+    def deduplicate_domain_blocks!
+      remove_index_if_exists!(:domain_blocks, 'index_domain_blocks_on_domain')
+
+      @prompt.say 'Deduplicating domain_allows…'
+      ActiveRecord::Base.connection.select_all("SELECT string_agg(id::text, ',') AS ids FROM domain_blocks GROUP BY domain HAVING count(*) > 1").each do |row|
+        domain_blocks = DomainBlock.where(id: row['ids'].split(',')).by_severity.reverse.to_a
+
+        reject_media = domain_blocks.any?(&:reject_media?)
+        reject_reports = domain_blocks.any?(&:reject_reports?)
+
+        reference_block = domain_blocks.shift
+
+        private_comment = domain_blocks.reduce(reference_block.private_comment.presence) { |a, b| a || b.private_comment.presence }
+        public_comment  = domain_blocks.reduce(reference_block.public_comment.presence)  { |a, b| a || b.public_comment.presence }
+
+        reference_block.update!(reject_media: reject_media, reject_reports: reject_reports, private_comment: private_comment, public_comment: public_comment)
+
+        domain_blocks.each(&:destroy)
+      end
+
+      @prompt.say 'Restoring domain_blocks indexes…'
+      ActiveRecord::Base.connection.add_index :domain_blocks, ['domain'], name: 'index_domain_blocks_on_domain', unique: true
+    end
+
+    def deduplicate_unavailable_domains!
+      return unless ActiveRecord::Base.connection.table_exists?(:unavailable_domains)
+
+      remove_index_if_exists!(:unavailable_domains, 'index_unavailable_domains_on_domain')
+
+      @prompt.say 'Deduplicating unavailable_domains…'
+      ActiveRecord::Base.connection.select_all("SELECT string_agg(id::text, ',') AS ids FROM unavailable_domains GROUP BY domain HAVING count(*) > 1").each do |row|
+        UnavailableDomain.where(id: row['ids'].split(',')).sort_by(&:id).reverse.drop(1).each(&:destroy)
+      end
+
+      @prompt.say 'Restoring domain_allows indexes…'
+      ActiveRecord::Base.connection.add_index :unavailable_domains, ['domain'], name: 'index_unavailable_domains_on_domain', unique: true
+    end
+
+    def deduplicate_email_domain_blocks!
+      remove_index_if_exists!(:email_domain_blocks, 'index_email_domain_blocks_on_domain')
+
+      @prompt.say 'Deduplicating email_domain_blocks…'
+      ActiveRecord::Base.connection.select_all("SELECT string_agg(id::text, ',') AS ids FROM email_domain_blocks GROUP BY domain HAVING count(*) > 1").each do |row|
+        domain_blocks = EmailDomainBlock.where(id: row['ids'].split(',')).sort_by { |b| b.parent.nil? ? 1 : 0 }.to_a
+        domain_blocks.drop(1).each(&:destroy)
+      end
+
+      @prompt.say 'Restoring email_domain_blocks indexes…'
+      ActiveRecord::Base.connection.add_index :email_domain_blocks, ['domain'], name: 'index_email_domain_blocks_on_domain', unique: true
+    end
+
+    def deduplicate_media_attachments!
+      remove_index_if_exists!(:media_attachments, 'index_media_attachments_on_shortcode')
+
+      @prompt.say 'Deduplicating media_attachments…'
+      ActiveRecord::Base.connection.select_all("SELECT string_agg(id::text, ',') AS ids FROM media_attachments WHERE shortcode IS NOT NULL GROUP BY shortcode HAVING count(*) > 1").each do |row|
+        MediaAttachment.where(id: row['ids'].split(',').drop(1)).update_all(shortcode: nil)
+      end
+
+      @prompt.say 'Restoring media_attachments indexes…'
+      ActiveRecord::Base.connection.add_index :media_attachments, ['shortcode'], name: 'index_media_attachments_on_shortcode', unique: true
+    end
+
+    def deduplicate_preview_cards!
+      remove_index_if_exists!(:preview_cards, 'index_preview_cards_on_url')
+
+      @prompt.say 'Deduplicating preview_cards…'
+      ActiveRecord::Base.connection.select_all("SELECT string_agg(id::text, ',') AS ids FROM preview_cards GROUP BY url HAVING count(*) > 1").each do |row|
+        PreviewCard.where(id: row['ids'].split(',')).sort_by(&:id).reverse.drop(1).each(&:destroy)
+      end
+
+      @prompt.say 'Restoring preview_cards indexes…'
+      ActiveRecord::Base.connection.add_index :preview_cards, ['url'], name: 'index_preview_cards_on_url', unique: true
+    end
+
+    def deduplicate_statuses!
+      remove_index_if_exists!(:statuses, 'index_statuses_on_uri')
+
+      @prompt.say 'Deduplicating statuses…'
+      ActiveRecord::Base.connection.select_all("SELECT string_agg(id::text, ',') AS ids FROM statuses WHERE uri IS NOT NULL GROUP BY uri HAVING count(*) > 1").each do |row|
+        statuses = Status.where(id: row['ids'].split(',')).sort_by(&:id)
+        ref_status = statuses.shift
+        statuses.each do |status|
+          merge_statuses!(ref_status, status) if status.account_id == ref_status.account_id
+          status.destroy
+        end
+      end
+
+      @prompt.say 'Restoring statuses indexes…'
+      ActiveRecord::Base.connection.add_index :statuses, ['uri'], name: 'index_statuses_on_uri', unique: true
+    end
+
+    def deduplicate_tags!
+      remove_index_if_exists!(:tags, 'index_tags_on_name_lower')
+
+      @prompt.say 'Deduplicating tags…'
+      ActiveRecord::Base.connection.select_all("SELECT string_agg(id::text, ',') AS ids FROM tags GROUP BY lower((name)::text) HAVING count(*) > 1").each do |row|
+        tags = Tag.where(id: row['ids'].split(',')).sort_by { |t| [t.usable?, t.trendable?, t.listable?].count(false) }
+        ref_tag = tags.shift
+        tags.each do |tag|
+          merge_tags!(ref_tag, tag)
+          tag.destroy
+        end
+      end
+
+      @prompt.say 'Restoring tags indexes…'
+      ActiveRecord::Base.connection.add_index :tags, 'lower((name)::text)', name: 'index_tags_on_name_lower', unique: true
+    end
+
+    def deduplicate_webauthn_credentials!
+      return unless ActiveRecord::Base.connection.table_exists?(:webauthn_credentials)
+
+      remove_index_if_exists!(:webauthn_credentials, 'index_webauthn_credentials_on_external_id')
+
+      @prompt.say 'Deduplicating webauthn_credentials…'
+      ActiveRecord::Base.connection.select_all("SELECT string_agg(id::text, ',') AS ids FROM webauthn_credentials GROUP BY external_id HAVING count(*) > 1").each do |row|
+        WebauthnCredential.where(id: row['ids'].split(',')).sort_by(&:id).reverse.drop(1).each(&:destroy)
+      end
+
+      @prompt.say 'Restoring webauthn_credentials indexes…'
+      ActiveRecord::Base.connection.add_index :webauthn_credentials, ['external_id'], name: 'index_webauthn_credentials_on_external_id', unique: true
+    end
+
+    def deduplicate_local_accounts!(accounts)
+      accounts = accounts.sort_by(&:id).reverse
+
+      @prompt.warn "Multiple local accounts were found for username '#{accounts.first.username}'."
+      @prompt.warn 'All those accounts are distinct accounts but only the most recently-created one is fully-functionnal.'
+
+      accounts.each_with_index do |account, idx|
+        @prompt.say '%2d. %s: created at: %s; updated at: %s; last logged in at: %s; statuses: %5d; last status at: %s' % [idx, account.username, account.created_at, account.updated_at, account.user&.last_sign_in_at&.to_s || 'N/A', account.account_stat&.statuses_count || 0, account.account_stat&.last_status_at || 'N/A']
+      end
+
+      @prompt.say 'Please chose the one to keep unchanged, other ones will be automatically renamed.'
+
+      ref_id = @prompt.ask('Account to keep unchanged:') do |q|
+        q.required true
+        q.default 0
+        q.convert :int
+      end
+
+      accounts.delete_at(ref_id)
+
+      i = 0
+      accounts.each do |account|
+        i += 1
+        username = account.username + "_#{i}"
+
+        while Account.local.exists?(username: username)
+          i += 1
+          username = account.username + "_#{i}"
+        end
+
+        account.update!(username: username)
+      end
+    end
+
+    def deduplicate_remote_accounts!(accounts)
+      accounts = accounts.sort_by(&:updated_at).reverse
+
+      reference_account = accounts.shift
+
+      accounts.each do |other_account|
+        if other_account.public_key == reference_account.public_key
+          # The accounts definitely point to the same resource, so
+          # it's safe to re-attribute content and relationships
+          reference_account.merge_with!(other_account)
+        end
+
+        other_account.destroy
+      end
+    end
+
+    def merge_conversations!(main_conv, duplicate_conv)
+      owned_classes = [ConversationMute, AccountConversation]
+      owned_classes.each do |klass|
+        klass.where(conversation_id: duplicate_conv.id).find_each do |record|
+          begin
+            record.update_attribute(:account_id, main_conv.id)
+          rescue ActiveRecord::RecordNotUnique
+            next
+          end
+        end
+      end
+    end
+
+    def merge_custom_emojis!(main_emoji, duplicate_emoji)
+      owned_classes = [AnnouncementReaction]
+      owned_classes.each do |klass|
+        klass.where(custom_emoji_id: duplicate_emoji.id).update_all(custom_emoji_id: main_emoji.id)
+      end
+    end
+
+    def merge_custom_emoji_categories!(main_category, duplicate_category)
+      owned_classes = [CustomEmoji]
+      owned_classes.each do |klass|
+        klass.where(category_id: duplicate_category.id).update_all(category_id: main_category.id)
+      end
+    end
+
+    def merge_statuses!(main_status, duplicate_status)
+      owned_classes = [Favourite, Mention, Poll]
+      owned_classes << Bookmark if ActiveRecord::Base.connection.table_exists?(:bookmarks)
+      owned_classes.each do |klass|
+        klass.where(status_id: duplicate_status.id).find_each do |record|
+          begin
+            record.update_attribute(:status_id, main_status.id)
+          rescue ActiveRecord::RecordNotUnique
+            next
+          end
+        end
+      end
+
+      StatusPin.where(account_id: main_status.account_id, status_id: duplicate_status.id).find_each do |record|
+        begin
+          record.update_attribute(:status_id, main_status.id)
+        rescue ActiveRecord::RecordNotUnique
+          next
+        end
+      end
+
+      Status.where(in_reply_to_id: duplicate_status.id).find_each do |record|
+        begin
+          record.update_attribute(:in_reply_to_id, main_status.id)
+        rescue ActiveRecord::RecordNotUnique
+          next
+        end
+      end
+
+      Status.where(reblog_of_id: duplicate_status.id).find_each do |record|
+        begin
+          record.update_attribute(:reblog_of_id, main_status.id)
+        rescue ActiveRecord::RecordNotUnique
+          next
+        end
+      end
+    end
+
+    def merge_tags!(main_tag, duplicate_tag)
+      [FeaturedTag].each do |klass|
+        klass.where(tag_id: duplicate_tag.id).find_each do |record|
+          begin
+            record.update_attribute(:tag_id, main_tag.id)
+          rescue ActiveRecord::RecordNotUnique
+            next
+          end
+        end
+      end
+    end
+
+    def find_duplicate_accounts
+      ActiveRecord::Base.connection.select_all("SELECT string_agg(id::text, ',') AS ids FROM accounts GROUP BY lower(username), COALESCE(lower(domain), '') HAVING count(*) > 1")
+    end
+
+    def remove_index_if_exists!(table, name)
+      ActiveRecord::Base.connection.remove_index(table, name: name)
+    rescue ArgumentError
+      nil
+    rescue ActiveRecord::StatementInvalid
+      nil
+    end
+  end
+end
diff --git a/lib/mastodon/version.rb b/lib/mastodon/version.rb
index 5e9270f74..4f23de2fb 100644
--- a/lib/mastodon/version.rb
+++ b/lib/mastodon/version.rb
@@ -13,7 +13,7 @@ module Mastodon
     end
 
     def patch
-      1
+      2
     end
 
     def flags
diff --git a/lib/paperclip/response_with_limit_adapter.rb b/lib/paperclip/response_with_limit_adapter.rb
index 8711b1349..17a2abd25 100644
--- a/lib/paperclip/response_with_limit_adapter.rb
+++ b/lib/paperclip/response_with_limit_adapter.rb
@@ -16,7 +16,7 @@ module Paperclip
     private
 
     def cache_current_values
-      @original_filename = filename_from_content_disposition || filename_from_path || 'data'
+      @original_filename = filename_from_content_disposition.presence || filename_from_path.presence || 'data'
       @size = @target.response.content_length
       @tempfile = copy_to_tempfile(@target)
       @content_type = ContentTypeDetector.new(@tempfile.path).detect
diff --git a/spec/controllers/auth/sessions_controller_spec.rb b/spec/controllers/auth/sessions_controller_spec.rb
index c387842cd..4560d64a8 100644
--- a/spec/controllers/auth/sessions_controller_spec.rb
+++ b/spec/controllers/auth/sessions_controller_spec.rb
@@ -215,7 +215,7 @@ RSpec.describe Auth::SessionsController, type: :controller do
 
       context 'using a valid OTP' do
         before do
-          post :create, params: { user: { otp_attempt: user.current_otp } }, session: { attempt_user_id: user.id }
+          post :create, params: { user: { otp_attempt: user.current_otp } }, session: { attempt_user_id: user.id, attempt_user_updated_at: user.updated_at.to_s }
         end
 
         it 'redirects to home' do
@@ -230,7 +230,7 @@ RSpec.describe Auth::SessionsController, type: :controller do
       context 'when the server has an decryption error' do
         before do
           allow_any_instance_of(User).to receive(:validate_and_consume_otp!).and_raise(OpenSSL::Cipher::CipherError)
-          post :create, params: { user: { otp_attempt: user.current_otp } }, session: { attempt_user_id: user.id }
+          post :create, params: { user: { otp_attempt: user.current_otp } }, session: { attempt_user_id: user.id, attempt_user_updated_at: user.updated_at.to_s }
         end
 
         it 'shows a login error' do
@@ -244,7 +244,7 @@ RSpec.describe Auth::SessionsController, type: :controller do
 
       context 'using a valid recovery code' do
         before do
-          post :create, params: { user: { otp_attempt: recovery_codes.first } }, session: { attempt_user_id: user.id }
+          post :create, params: { user: { otp_attempt: recovery_codes.first } }, session: { attempt_user_id: user.id, attempt_user_updated_at: user.updated_at.to_s }
         end
 
         it 'redirects to home' do
@@ -258,7 +258,7 @@ RSpec.describe Auth::SessionsController, type: :controller do
 
       context 'using an invalid OTP' do
         before do
-          post :create, params: { user: { otp_attempt: 'wrongotp' } }, session: { attempt_user_id: user.id }
+          post :create, params: { user: { otp_attempt: 'wrongotp' } }, session: { attempt_user_id: user.id, attempt_user_updated_at: user.updated_at.to_s }
         end
 
         it 'shows a login error' do
@@ -302,7 +302,7 @@ RSpec.describe Auth::SessionsController, type: :controller do
       context 'using a valid sign in token' do
         before do
           user.generate_sign_in_token && user.save
-          post :create, params: { user: { sign_in_token_attempt: user.sign_in_token } }, session: { attempt_user_id: user.id }
+          post :create, params: { user: { sign_in_token_attempt: user.sign_in_token } }, session: { attempt_user_id: user.id, attempt_user_updated_at: user.updated_at.to_s }
         end
 
         it 'redirects to home' do
@@ -316,7 +316,7 @@ RSpec.describe Auth::SessionsController, type: :controller do
 
       context 'using an invalid sign in token' do
         before do
-          post :create, params: { user: { sign_in_token_attempt: 'wrongotp' } }, session: { attempt_user_id: user.id }
+          post :create, params: { user: { sign_in_token_attempt: 'wrongotp' } }, session: { attempt_user_id: user.id, attempt_user_updated_at: user.updated_at.to_s }
         end
 
         it 'shows a login error' do
diff --git a/spec/models/account_spec.rb b/spec/models/account_spec.rb
index 98d29e6f3..75f628076 100644
--- a/spec/models/account_spec.rb
+++ b/spec/models/account_spec.rb
@@ -817,4 +817,27 @@ RSpec.describe Account, type: :model do
 
   include_examples 'AccountAvatar', :account
   include_examples 'AccountHeader', :account
+
+  describe '#increment_count!' do
+    subject { Fabricate(:account) }
+
+    it 'increments the count in multi-threaded an environment when account_stat is not yet initialized' do
+      subject
+
+      increment_by   = 15
+      wait_for_start = true
+
+      threads = Array.new(increment_by) do
+        Thread.new do
+          true while wait_for_start
+          Account.find(subject.id).increment_count!(:followers_count)
+        end
+      end
+
+      wait_for_start = false
+      threads.each(&:join)
+
+      expect(subject.reload.followers_count).to eq 15
+    end
+  end
 end
diff --git a/spec/services/resolve_account_service_spec.rb b/spec/services/resolve_account_service_spec.rb
index cea942e39..92c837050 100644
--- a/spec/services/resolve_account_service_spec.rb
+++ b/spec/services/resolve_account_service_spec.rb
@@ -4,23 +4,76 @@ RSpec.describe ResolveAccountService, type: :service do
   subject { described_class.new }
 
   before do
-    stub_request(:get, "https://quitter.no/.well-known/host-meta").to_return(request_fixture('.host-meta.txt'))
-    stub_request(:get, "https://example.com/.well-known/webfinger?resource=acct:catsrgr8@example.com").to_return(status: 404)
     stub_request(:get, "https://example.com/.well-known/host-meta").to_return(status: 404)
     stub_request(:get, "https://quitter.no/avatar/7477-300-20160211190340.png").to_return(request_fixture('avatar.txt'))
-    stub_request(:get, "https://quitter.no/.well-known/webfinger?resource=acct:catsrgr8@quitter.no").to_return(status: 404)
     stub_request(:get, "https://ap.example.com/.well-known/webfinger?resource=acct:foo@ap.example.com").to_return(request_fixture('activitypub-webfinger.txt'))
     stub_request(:get, "https://ap.example.com/users/foo").to_return(request_fixture('activitypub-actor.txt'))
     stub_request(:get, "https://ap.example.com/users/foo.atom").to_return(request_fixture('activitypub-feed.txt'))
     stub_request(:get, %r{https://ap.example.com/users/foo/\w+}).to_return(status: 404)
   end
 
-  it 'raises error if no such user can be resolved via webfinger' do
-    expect(subject.call('catsrgr8@quitter.no')).to be_nil
+  context 'when there is an LRDD endpoint but no resolvable account' do
+    before do
+      stub_request(:get, "https://quitter.no/.well-known/host-meta").to_return(request_fixture('.host-meta.txt'))
+      stub_request(:get, "https://quitter.no/.well-known/webfinger?resource=acct:catsrgr8@quitter.no").to_return(status: 404)
+    end
+
+    it 'returns nil' do
+      expect(subject.call('catsrgr8@quitter.no')).to be_nil
+    end
   end
 
-  it 'raises error if the domain does not have webfinger' do
-    expect(subject.call('catsrgr8@example.com')).to be_nil
+  context 'when there is no LRDD endpoint nor resolvable account' do
+    before do
+      stub_request(:get, "https://example.com/.well-known/webfinger?resource=acct:catsrgr8@example.com").to_return(status: 404)
+    end
+
+    it 'returns nil' do
+      expect(subject.call('catsrgr8@example.com')).to be_nil
+    end
+  end
+
+  context 'with a legitimate webfinger redirection' do
+    before do
+      webfinger = { subject: 'acct:foo@ap.example.com', links: [{ rel: 'self', href: 'https://ap.example.com/users/foo', type: 'application/activity+json' }] }
+      stub_request(:get, 'https://redirected.example.com/.well-known/webfinger?resource=acct:Foo@redirected.example.com').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
+    end
+
+    it 'returns new remote account' do
+      account = subject.call('Foo@redirected.example.com')
+
+      expect(account.activitypub?).to eq true
+      expect(account.acct).to eq 'foo@ap.example.com'
+      expect(account.inbox_url).to eq 'https://ap.example.com/users/foo/inbox'
+    end
+  end
+
+  context 'with a misconfigured redirection' do
+    before do
+      webfinger = { subject: 'acct:Foo@redirected.example.com', links: [{ rel: 'self', href: 'https://ap.example.com/users/foo', type: 'application/activity+json' }] }
+      stub_request(:get, 'https://redirected.example.com/.well-known/webfinger?resource=acct:Foo@redirected.example.com').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
+    end
+
+    it 'returns new remote account' do
+      account = subject.call('Foo@redirected.example.com')
+
+      expect(account.activitypub?).to eq true
+      expect(account.acct).to eq 'foo@ap.example.com'
+      expect(account.inbox_url).to eq 'https://ap.example.com/users/foo/inbox'
+    end
+  end
+
+  context 'with too many webfinger redirections' do
+    before do
+      webfinger = { subject: 'acct:foo@evil.example.com', links: [{ rel: 'self', href: 'https://ap.example.com/users/foo', type: 'application/activity+json' }] }
+      stub_request(:get, 'https://redirected.example.com/.well-known/webfinger?resource=acct:Foo@redirected.example.com').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
+      webfinger2 = { subject: 'acct:foo@ap.example.com', links: [{ rel: 'self', href: 'https://ap.example.com/users/foo', type: 'application/activity+json' }] }
+      stub_request(:get, 'https://evil.example.com/.well-known/webfinger?resource=acct:foo@evil.example.com').to_return(body: Oj.dump(webfinger2), headers: { 'Content-Type': 'application/jrd+json' })
+    end
+
+    it 'returns nil' do
+      expect(subject.call('Foo@redirected.example.com')).to be_nil
+    end
   end
 
   context 'with an ActivityPub account' do