Add index on deployable_type/id for deployments

changelogs/unreleased/add-missing-index-for-deployments.yml

+---
+title: Add index on deployable_type/id for deployments
+merge_request:
+author:
+type: performance

db/migrate/20180626125654_add_index_on_deployable_for_deployments.rb

+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class AddIndexOnDeployableForDeployments < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_index :deployments, [:deployable_type, :deployable_id]
+  end
+
+  def down
+    remove_concurrent_index :deployments, [:deployable_type, :deployable_id]
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
-ActiveRecord::Schema.define(version: 20180608201435) do
+ActiveRecord::Schema.define(version: 20180626125654) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -757,6 +757,7 @@ ActiveRecord::Schema.define(version: 20180608201435) do
   end
   add_index "deployments", ["created_at"], name: "index_deployments_on_created_at", using: :btree
+  add_index "deployments", ["deployable_type", "deployable_id"], name: "index_deployments_on_deployable_type_and_deployable_id", using: :btree
   add_index "deployments", ["environment_id", "id"], name: "index_deployments_on_environment_id_and_id", using: :btree
   add_index "deployments", ["environment_id", "iid", "project_id"], name: "index_deployments_on_environment_id_and_iid_and_project_id", using: :btree
   add_index "deployments", ["project_id", "iid"], name: "index_deployments_on_project_id_and_iid", unique: true, using: :btree