Add lower path index to redirect_routes

changelogs/unreleased/mk-add-lower-path-index-to-redirect-routes.yml

+---
+title: Improve redirect route query performance
+merge_request: 13062
+author:

db/migrate/20170724214302_add_lower_path_index_to_redirect_routes.rb

+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class AddLowerPathIndexToRedirectRoutes < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+  INDEX_NAME = 'index_on_redirect_routes_lower_path'
+
+  disable_ddl_transaction!
+
+  def up
+    return unless Gitlab::Database.postgresql?
+
+    execute "CREATE INDEX CONCURRENTLY #{INDEX_NAME} ON redirect_routes (LOWER(path));"
+  end
+
+  def down
+    return unless Gitlab::Database.postgresql?
+
+    # Why not use remove_concurrent_index_by_name?
+    #
+    # `index_exists?` doesn't work on this index. Perhaps this is related to the
+    # fact that the index doesn't show up in the schema. And apparently it isn't
+    # trivial to write a query that checks for an index. BUT there is a
+    # convenient `IF EXISTS` parameter for `DROP INDEX`.
+    if supports_drop_index_concurrently?
+      disable_statement_timeout
+      execute "DROP INDEX CONCURRENTLY IF EXISTS #{INDEX_NAME};"
+    else
+      execute "DROP INDEX IF EXISTS #{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: 20170717150329) do
+ActiveRecord::Schema.define(version: 20170724214302) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"

lib/tasks/migrate/setup_postgresql.rake

@@ -4,6 +4,7 @@ require Rails.root.join('db/migrate/20151007120511_namespaces_projects_path_lowe
 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')
+require Rails.root.join('db/migrate/20170724214302_add_lower_path_index_to_redirect_routes')
 require Rails.root.join('db/migrate/20170503185032_index_redirect_routes_path_for_like')
 
 desc 'GitLab | Sets up PostgreSQL'
@@ -12,5 +13,6 @@ task setup_postgresql: :environment do
   AddUsersLowerUsernameEmailIndexes.new.up
   AddLowerPathIndexToRoutes.new.up
   IndexRoutesPathForLike.new.up
+  AddLowerPathIndexToRedirectRoutes.new.up
   IndexRedirectRoutesPathForLike.new.up
 end