Add temporary index for PA data migration

db/migrate/20190918104212_add_merge_request_metrics_merged_at_index.rb

+# frozen_string_literal: true
+
+class AddMergeRequestMetricsMergedAtIndex < ActiveRecord::Migration[5.2]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_index :merge_request_metrics, [:merged_at, :id]
+  end
+
+  def down
+    remove_concurrent_index :merge_request_metrics, [:merged_at, :id]
+  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_09_14_223900) do
+ActiveRecord::Schema.define(version: 2019_09_18_104222) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "pg_trgm"
@@ -2120,6 +2120,7 @@ ActiveRecord::Schema.define(version: 2019_09_14_223900) do
     t.index ["latest_closed_by_id"], name: "index_merge_request_metrics_on_latest_closed_by_id"
     t.index ["merge_request_id", "merged_at"], name: "index_merge_request_metrics_on_merge_request_id_and_merged_at", where: "(merged_at IS NOT NULL)"
     t.index ["merge_request_id"], name: "index_merge_request_metrics"
+    t.index ["merged_at", "id"], name: "index_merge_request_metrics_on_merged_at_and_id"
     t.index ["merged_by_id"], name: "index_merge_request_metrics_on_merged_by_id"
     t.index ["pipeline_id"], name: "index_merge_request_metrics_on_pipeline_id"
   end