Optimise searching for users using short queries

app/models/user.rb

@@ -327,8 +327,8 @@ class User < ActiveRecord::Base
       SQL
 
       where(
-        fuzzy_arel_match(:name, query)
-          .or(fuzzy_arel_match(:username, query))
+        fuzzy_arel_match(:name, query, lower_exact_match: true)
+          .or(fuzzy_arel_match(:username, query, lower_exact_match: true))
           .or(arel_table[:email].eq(query))
       ).reorder(order % { query: ActiveRecord::Base.connection.quote(query) }, :name)
     end

db/migrate/20180215181245_users_name_lower_index.rb

+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class UsersNameLowerIndex < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  # Set this constant to true if this migration requires downtime.
+  DOWNTIME = false
+  INDEX_NAME = 'index_on_users_name_lower'
+
+  disable_ddl_transaction!
+
+  def up
+    return unless Gitlab::Database.postgresql?
+
+    # On GitLab.com this produces an index with a size of roughly 60 MB.
+    execute "CREATE INDEX CONCURRENTLY #{INDEX_NAME} ON users (LOWER(name))"
+  end
+
+  def down
+    return unless Gitlab::Database.postgresql?
+
+    if supports_drop_index_concurrently?
+      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: 20180213131630) do
+ActiveRecord::Schema.define(version: 20180215181245) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"

lib/gitlab/sql/pattern.rb

@@ -25,7 +25,11 @@ module Gitlab
           query.length >= MIN_CHARS_FOR_PARTIAL_MATCHING
         end
 
-        def fuzzy_arel_match(column, query)
+        # column - The column name to search in.
+        # query - The text to search for.
+        # lower_exact_match - When set to `true` we'll fall back to using
+        #                     `LOWER(column) = query` instead of using `ILIKE`.
+        def fuzzy_arel_match(column, query, lower_exact_match: false)
           query = query.squish
           return nil unless query.present?
 
@@ -34,9 +38,17 @@ module Gitlab
           if words.any?
             words.map { |word| arel_table[column].matches(to_pattern(word)) }.reduce(:and)
           else
+            sanitized_query = sanitize_sql_like(query)
+
             # No words of at least 3 chars, but we can search for an exact
             # case insensitive match with the query as a whole
-            arel_table[column].matches(sanitize_sql_like(query))
+            if lower_exact_match
+              Arel::Nodes::NamedFunction
+                .new('LOWER', [arel_table[column]])
+                .eq(sanitized_query)
+            else
+              arel_table[column].matches(sanitized_query)
+            end
           end
         end
 

lib/tasks/migrate/setup_postgresql.rake

@@ -8,6 +8,7 @@ task setup_postgresql: :environment do
   require Rails.root.join('db/migrate/20170503185032_index_redirect_routes_path_for_like')
   require Rails.root.join('db/migrate/20171220191323_add_index_on_namespaces_lower_name.rb')
   require Rails.root.join('db/migrate/20180113220114_rework_redirect_routes_indexes.rb')
+  require Rails.root.join('db/migrate/20180215181245_users_name_lower_index.rb')
 
   NamespacesProjectsPathLowerIndexes.new.up
   AddUsersLowerUsernameEmailIndexes.new.up
@@ -17,4 +18,5 @@ task setup_postgresql: :environment do
   IndexRedirectRoutesPathForLike.new.up
   AddIndexOnNamespacesLowerName.new.up
   ReworkRedirectRoutesIndexes.new.up
+  UsersNameLowerIndex.new.up
 end

spec/lib/gitlab/sql/pattern_spec.rb

@@ -154,6 +154,12 @@ describe Gitlab::SQL::Pattern do
       it 'returns a single equality condition' do
         expect(fuzzy_arel_match.to_sql).to match(/title.*I?LIKE 'fo'/)
       end
+
+      it 'uses LOWER instead of ILIKE when LOWER is enabled' do
+        rel = Issue.fuzzy_arel_match(:title, query, lower_exact_match: true)
+
+        expect(rel.to_sql).to match(/LOWER\(.*title.*\).*=.*'fo'/)
+      end
     end
 
     context 'with two words both equal to 3 chars' do