remove chat tables & adjust status table index

db/migrate/20190724173350_remove_chat.rb

@@ -0,0 +1,15 @@
+class RemoveChat < ActiveRecord::Migration[5.2]
+  def up
+    Status.where(visibility: 6).find_each &:destroy
+    remove_index :statuses, name: "index_statuses_on_account_id_and_id_and_visibility"
+    safety_assured {
+      remove_column :accounts, :supports_chat
+      remove_column :tags, :chat
+      drop_table :chat_accounts
+    }
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end

db/migrate/20190724175247_add_public_index_to_statuses.rb

@@ -0,0 +1,6 @@
+class AddPublicIndexToStatuses < ActiveRecord::Migration[5.2]
+  disable_ddl_transaction!
+  def change
+    add_index :statuses, [:account_id, :id, :visibility], where: 'visibility IN (0, 1, 2, 4)', order: { id: :desc }, algorithm: :concurrently
+  end
+end