Add LIKE index for routes.path

Nested groups support uses queries along the lines of `path LIKE 'X/%'`.
For these queries to use an index on PostgreSQL we need to use either
the varchar_pattern_ops or text_pattern_ops operator class.

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/29554

db/migrate/20170317203554_index_routes_path_for_like.rb

+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class IndexRoutesPathForLike < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  # Set this constant to true if this migration requires downtime.
+  DOWNTIME = false
+
+  INDEX_NAME = 'index_routes_on_path_text_pattern_ops'
+
+  disable_ddl_transaction!
+
+  def up
+    return unless Gitlab::Database.postgresql?
+
+    unless index_exists?(:routes, name: INDEX_NAME)
+      execute("CREATE INDEX CONCURRENTLY #{INDEX_NAME} ON routes (path varchar_pattern_ops);")
+    end
+  end
+
+  def down
+    return unless Gitlab::Database.postgresql?
+
+    if index_exists?(:routes, name: INDEX_NAME)
+      execute("DROP INDEX CONCURRENTLY #{INDEX_NAME};")
+    end
+  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: 20170315174634) do
+ActiveRecord::Schema.define(version: 20170317203554) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -1070,6 +1070,7 @@ ActiveRecord::Schema.define(version: 20170315174634) do
   end
   add_index "routes", ["path"], name: "index_routes_on_path", unique: true, using: :btree
+  add_index "routes", ["path"], name: "index_routes_on_path_text_pattern_ops", using: :btree, opclasses: {"path"=>"varchar_pattern_ops"}
   add_index "routes", ["source_type", "source_id"], name: "index_routes_on_source_type_and_source_id", unique: true, using: :btree
   create_table "sent_notifications", force: :cascade do |t|

lib/tasks/migrate/setup_postgresql.rake

@@ -3,10 +3,12 @@ require Rails.root.join('lib/gitlab/database/migration_helpers')
 require Rails.root.join('db/migrate/20151007120511_namespaces_projects_path_lower_indexes')
 require Rails.root.join('db/migrate/20151008110232_add_users_lower_username_email_indexes')
 require Rails.root.join('db/migrate/20161212142807_add_lower_path_index_to_routes')
+require Rails.root.join('db/migrate/20170317203554_index_routes_path_for_like')
 desc 'GitLab | Sets up PostgreSQL'
 task setup_postgresql: :environment do
   NamespacesProjectsPathLowerIndexes.new.up
   AddUsersLowerUsernameEmailIndexes.new.up
   AddLowerPathIndexToRoutes.new.up
+  IndexRoutesPathForLike.new.up
 end