Remove redundant index for GitLab.com

* index_push_rules_is_sample
* index_project_mirror_data_on_next_execution_timestamp

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: 20181126153547) do
+ActiveRecord::Schema.define(version: 20181203154104) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"

ee/changelogs/unreleased/53989-remove-redundant-index.yml

+---
+title: Remove redundant indices for is_sample on push_rules and next_execution_timestamp on project_mirror_data
+merge_request: 8695
+author:
+type: performance

ee/db/migrate/20181203154104_remove_redundant_indices_for_project_mirror_data_and_push_rules.rb

+# frozen_string_literal: true
+
+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class RemoveRedundantIndicesForProjectMirrorDataAndPushRules < ActiveRecord::Migration[5.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    remove_concurrent_index(*index_on_project_mirror_data)
+    remove_concurrent_index(*index_on_push_rules)
+  end
+
+  def down
+    add_concurrent_index(*index_on_push_rules)
+    add_concurrent_index(*index_on_project_mirror_data)
+  end
+
+  private
+
+  def index_on_project_mirror_data
+    [
+      :project_mirror_data,
+      [:next_execution_timestamp],
+      { name: 'index_project_mirror_data_on_next_execution_timestamp' }
+    ]
+  end
+
+  def index_on_push_rules
+    [
+      :push_rules,
+      [:is_sample],
+      { name: 'index_push_rules_is_sample' }
+    ]
+  end
+end