Change index on ci_builds to optimize Jobs Controller

changelogs/unreleased/add-ci-builds-index-for-jobscontroller.yml

+---
+title: Change index on ci_builds to optimize Jobs Controller
+merge_request:
+author:
+type: other

db/migrate/20170927095921_add_ci_builds_index_for_jobscontroller.rb

+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class AddCiBuildsIndexForJobscontroller < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  # Set this constant to true if this migration requires downtime.
+  DOWNTIME = false
+
+  # When a migration requires downtime you **must** uncomment the following
+  # constant and define a short and easy to understand explanation as to why the
+  # migration requires downtime.
+  # DOWNTIME_REASON = ''
+
+  # When using the methods "add_concurrent_index", "remove_concurrent_index" or
+  # "add_column_with_default" you must disable the use of transactions
+  # as these methods can not run in an existing transaction.
+  # When using "add_concurrent_index" or "remove_concurrent_index" methods make sure
+  # that either of them is the _only_ method called in the migration,
+  # any other changes should go in a separate migration.
+  # This ensures that upon failure _only_ the index creation or removing fails
+  # and can be retried or reverted easily.
+  #
+  # To disable transactions uncomment the following line and remove these
+  # comments:
+  # disable_ddl_transaction!
+
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_index :ci_builds, [:project_id, :id]  unless index_exists? :ci_builds, [:project_id, :id]
+    remove_concurrent_index :ci_builds, :project_id if index_exists? :ci_builds, :project_id
+  end
+
+  def down
+    add_concurrent_index :ci_builds, :project_id unless index_exists? :ci_builds, :project_id
+    remove_concurrent_index :ci_builds, [:project_id, :id] if index_exists? :ci_builds, [:project_id, :id]
+  end
+end

db/schema.rb

@@ -256,7 +256,7 @@ ActiveRecord::Schema.define(version: 20170928100231) do
   add_index "ci_builds", ["commit_id", "status", "type"], name: "index_ci_builds_on_commit_id_and_status_and_type", using: :btree
   add_index "ci_builds", ["commit_id", "type", "name", "ref"], name: "index_ci_builds_on_commit_id_and_type_and_name_and_ref", using: :btree
   add_index "ci_builds", ["commit_id", "type", "ref"], name: "index_ci_builds_on_commit_id_and_type_and_ref", using: :btree
-  add_index "ci_builds", ["project_id"], name: "index_ci_builds_on_project_id", using: :btree
+  add_index "ci_builds", ["project_id", "id"], name: "index_ci_builds_on_project_id_and_id", using: :btree
   add_index "ci_builds", ["protected"], name: "index_ci_builds_on_protected", using: :btree
   add_index "ci_builds", ["runner_id"], name: "index_ci_builds_on_runner_id", using: :btree
   add_index "ci_builds", ["stage_id"], name: "index_ci_builds_on_stage_id", using: :btree