Composite metric identifier index

Use project_id and identifier for composite prometheus_metric index.

app/models/prometheus_metric.rb

@@ -11,6 +11,7 @@ class PrometheusMetric < ApplicationRecord
   validates :group, presence: true
   validates :y_label, presence: true
   validates :unit, presence: true
+  validates :identifier, uniqueness: { scope: :project_id }, allow_nil: true
 
   validates :project, presence: true, unless: :common?
   validates :project, absence: true, if: :common?

changelogs/unreleased/rc-enforce_unique_metrics_id_across_project.yml

+---
+title: Enforce prometheus metric uniqueness across project scope
+merge_request: 35566
+author:
+type: fixed

db/migrate/20200629192638_add_uniq_index_on_metric_identifier_and_project_id.rb

+# frozen_string_literal: true
+
+class AddUniqIndexOnMetricIdentifierAndProjectId < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_index :prometheus_metrics, [:identifier, :project_id], unique: true
+  end
+
+  def down
+    remove_concurrent_index :prometheus_metrics, [:identifier, :project_id]
+  end
+end

db/structure.sql

@@ -19931,6 +19931,8 @@ CREATE INDEX index_prometheus_metrics_on_group ON public.prometheus_metrics USIN
 
 CREATE UNIQUE INDEX index_prometheus_metrics_on_identifier ON public.prometheus_metrics USING btree (identifier);
 
+CREATE UNIQUE INDEX index_prometheus_metrics_on_identifier_and_project_id ON public.prometheus_metrics USING btree (identifier, project_id);
+
 CREATE INDEX index_prometheus_metrics_on_project_id ON public.prometheus_metrics USING btree (project_id);
 
 CREATE INDEX index_protected_branch_merge_access ON public.protected_branch_merge_access_levels USING btree (protected_branch_id);
@@ -23583,6 +23585,7 @@ COPY "schema_migrations" (version) FROM STDIN;
 20200626130220
 20200630110826
 20200701093859
+20200629192638
 20200702123805
 20200703154822
 20200704143633

spec/models/prometheus_metric_spec.rb

@@ -11,6 +11,7 @@ RSpec.describe PrometheusMetric do
   it { is_expected.to validate_presence_of(:title) }
   it { is_expected.to validate_presence_of(:query) }
   it { is_expected.to validate_presence_of(:group) }
+  it { is_expected.to validate_uniqueness_of(:identifier).scoped_to(:project_id).allow_nil }
 
   describe 'common metrics' do
     using RSpec::Parameterized::TableSyntax