Improve account index migration (#7684)

* Improve account index migration

- Display more progress in stdout
- Catch PG::UniqueViolation when re-attributing favourites
- Skip callbacks and validations when re-attributing other relationships

* Use in_batches to reduce table lock-up during account merge

* Use #say_with_time to benchmark each deduplication

db/migrate/20180528141303_fix_accounts_unique_index.rb

@@ -39,6 +39,7 @@ class FixAccountsUniqueIndex < ActiveRecord::Migration[5.2]
     accounts          = accounts.first.local? ? accounts.sort_by(&:created_at) : accounts.sort_by(&:updated_at).reverse
     reference_account = accounts.shift
 
+    say_with_time "Deduplicating @#{reference_account.acct} (#{accounts.size} duplicates)..." do
       accounts.each do |other_account|
         if other_account.public_key == reference_account.public_key
           # The accounts definitely point to the same resource, so
@@ -55,10 +56,11 @@ class FixAccountsUniqueIndex < ActiveRecord::Migration[5.2]
         other_account.destroy
       end
     end
+  end
 
   def merge_accounts!(main_account, duplicate_account)
-    [Status, Favourite, Mention, StatusPin, StreamEntry].each do |klass|
-      klass.where(account_id: duplicate_account.id).update_all(account_id: main_account.id)
+    [Status, Mention, StatusPin, StreamEntry].each do |klass|
+      klass.where(account_id: duplicate_account.id).in_batches.update_all(account_id: main_account.id)
     end
 
     # Since it's the same remote resource, the remote resource likely
@@ -67,19 +69,19 @@ class FixAccountsUniqueIndex < ActiveRecord::Migration[5.2]
     # 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
-    [Follow, FollowRequest, Block, Mute].each do |klass|
+    [Favourite, Follow, FollowRequest, Block, Mute].each do |klass|
       klass.where(account_id: duplicate_account.id).find_each do |record|
         begin
-          record.update(account_id: main_account.id)
-        rescue ActiveRecord::RecordNotUnique
+          record.update_attribute(:account_id, main_account.id)
+        rescue PG::UniqueViolation
           next
         end
       end
 
       klass.where(target_account_id: duplicate_account.id).find_each do |record|
         begin
-          record.update(target_account_id: main_account.id)
-        rescue ActiveRecord::RecordNotUnique
+          record.update_attribute(:target_account_id, main_account.id)
+        rescue PG::UniqueViolation
           next
         end
       end