Fix slow local timeline query (mastodon#11648)

Fix mastodon#11643

Author: Gargron

db/migrate/20190823221802_add_local_index_to_statuses.rb

@@ -0,0 +1,11 @@
+class AddLocalIndexToStatuses < ActiveRecord::Migration[5.2]
+  disable_ddl_transaction!
+
+  def up
+    add_index :statuses, [:id, :account_id], name: :index_statuses_local_20190824, algorithm: :concurrently, order: { id: :desc }, where: '(local OR (uri IS NULL)) AND deleted_at IS NULL AND visibility = 0 AND reblog_of_id IS NULL AND ((NOT reply) OR (in_reply_to_account_id = account_id))'
+  end
+
+  def down
+    remove_index :statuses, name: :index_statuses_local_20190824
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 2019_08_20_003045) do
+ActiveRecord::Schema.define(version: 2019_08_23_221802) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -647,6 +647,7 @@
     t.bigint "poll_id"
     t.datetime "deleted_at"
     t.index ["account_id", "id", "visibility", "updated_at"], name: "index_statuses_20190820", order: { id: :desc }, where: "(deleted_at IS NULL)"
+    t.index ["id", "account_id"], name: "index_statuses_local_20190824", order: { id: :desc }, where: "((local OR (uri IS NULL)) AND (deleted_at IS NULL) AND (visibility = 0) AND (reblog_of_id IS NULL) AND ((NOT reply) OR (in_reply_to_account_id = account_id)))"
     t.index ["in_reply_to_account_id"], name: "index_statuses_on_in_reply_to_account_id"
     t.index ["in_reply_to_id"], name: "index_statuses_on_in_reply_to_id"
     t.index ["reblog_of_id", "account_id"], name: "index_statuses_on_reblog_of_id_and_account_id"