Use limit for search count queries

Search query is especially slow if a user searches a generic string
which matches many records, in such case search can take tens of
seconds or time out. To speed up the search query, we search only for
first 1000 records, if there is >1000 matching records we just display
"1000+" instead of precise total count supposing that with such amount
the exact count is not so important for the user.

Because for issues even limited search was not fast enough, 2-phase
approach is used for issues: first we use simpler/faster query to get
all public issues, if this exceeds the limit, we just return the limit.
If the amount of matching results is lower than limit, we re-run more
complex search query (which includes also confidential issues).
Re-running the complex query should be fast enough in such case because the
amount of matching issues is lower than limit.

Because exact total_count is now limited, this patch also switches to
to "prev/next" pagination.

Related #40540

app/finders/issues_finder.rb

@@ -15,6 +15,7 @@
 #     label_name: string
 #     sort: string
 #     my_reaction_emoji: string
+#     public_only: boolean
 #
 class IssuesFinder < IssuableFinder
   CONFIDENTIAL_ACCESS_LEVEL = Gitlab::Access::REPORTER
@@ -40,7 +41,15 @@ class IssuesFinder < IssuableFinder
   private
 
   def init_collection
-    with_confidentiality_access_check
+    if public_only?
+      Issue.public_only
+    else
+      with_confidentiality_access_check
+    end
+  end
+
+  def public_only?
+    params.fetch(:public_only, false)
   end
 
   def user_can_see_all_confidential_issues?

app/helpers/search_helper.rb

@@ -170,4 +170,8 @@ module SearchHelper
     # Truncato's filtered_tags and filtered_attributes are not quite the same
     sanitize(html, tags: %w(a p ol ul li pre code))
   end
+
+  def limited_count(count, limit = 1000)
+    count > limit ? "#{limit}+" : count
+  end
 end

app/views/search/_category.html.haml

@@ -57,25 +57,24 @@
           Titles and Filenames
           %span.badge
             = @search_results.snippet_titles_count
-
     - else
       %li{ class: active_when(@scope == 'projects') }
         = link_to search_filter_path(scope: 'projects') do
           Projects
           %span.badge
-            = @search_results.projects_count
+            = limited_count(@search_results.limited_projects_count)
       %li{ class: active_when(@scope == 'issues') }
         = link_to search_filter_path(scope: 'issues') do
           Issues
           %span.badge
-            = @search_results.issues_count
+            = limited_count(@search_results.limited_issues_count)
       %li{ class: active_when(@scope == 'merge_requests') }
         = link_to search_filter_path(scope: 'merge_requests') do
           Merge requests
           %span.badge
-            = @search_results.merge_requests_count
+            = limited_count(@search_results.limited_merge_requests_count)
       %li{ class: active_when(@scope == 'milestones') }
         = link_to search_filter_path(scope: 'milestones') do
           Milestones
           %span.badge
-            = @search_results.milestones_count
+            = limited_count(@search_results.limited_milestones_count)

app/views/search/_results.html.haml

@@ -2,7 +2,8 @@
   = render partial: "search/results/empty"
 - else
   .row-content-block
-    = search_entries_info(@search_objects, @scope, @search_term)
+    - unless @search_objects.is_a?(Kaminari::PaginatableWithoutCount)
+      = search_entries_info(@search_objects, @scope, @search_term)
     - unless @show_snippets
       - if @project
         in project #{link_to @project.name_with_namespace, [@project.namespace.becomes(Namespace), @project]}
@@ -22,4 +23,4 @@
           = render partial: "search/results/#{@scope.singularize}", collection: @search_objects
 
     - if @scope != 'projects'
-      = paginate(@search_objects, theme: 'gitlab')
+      = paginate_collection(@search_objects)

changelogs/unreleased/40540-use-limit-for-global-search.yml

+---
+title: Optimize search queries on the search page by setting a limit for matching records.
+merge_request:
+author:
+type: performance

db/migrate/20180115201419_add_index_updated_at_to_issues.rb

+class AddIndexUpdatedAtToIssues < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_index :issues, :updated_at
+  end
+
+  def down
+    remove_concurrent_index :issues, :updated_at
+  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: 20180113220114) do
+ActiveRecord::Schema.define(version: 20180115201419) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -886,6 +886,7 @@ ActiveRecord::Schema.define(version: 20180113220114) do
   add_index "issues", ["relative_position"], name: "index_issues_on_relative_position", using: :btree
   add_index "issues", ["state"], name: "index_issues_on_state", using: :btree
   add_index "issues", ["title"], name: "index_issues_on_title_trigram", using: :gin, opclasses: {"title"=>"gin_trgm_ops"}
+  add_index "issues", ["updated_at"], name: "index_issues_on_updated_at", using: :btree
   add_index "issues", ["updated_by_id"], name: "index_issues_on_updated_by_id", where: "(updated_by_id IS NOT NULL)", using: :btree
 
   create_table "keys", force: :cascade do |t|

lib/api/v3/projects.rb

@@ -175,7 +175,7 @@ module API
         end
         get "/search/:query", requirements: { query: /[^\/]+/ } do
           search_service = Search::GlobalService.new(current_user, search: params[:query]).execute
-          projects = search_service.objects('projects', params[:page])
+          projects = search_service.objects('projects', params[:page], false)
           projects = projects.reorder(params[:order_by] => params[:sort])
 
           present paginate(projects), with: ::API::V3::Entities::Project

lib/gitlab/project_search_results.rb

@@ -20,7 +20,7 @@ module Gitlab
       when 'commits'
         Kaminari.paginate_array(commits).page(page).per(per_page)
       else
-        super
+        super(scope, page, false)
       end
     end
 

lib/gitlab/search_results.rb

@@ -40,19 +40,21 @@ module Gitlab
       @default_project_filter = default_project_filter
     end
 
-    def objects(scope, page = nil)
-      case scope
-      when 'projects'
-        projects.page(page).per(per_page)
-      when 'issues'
-        issues.page(page).per(per_page)
-      when 'merge_requests'
-        merge_requests.page(page).per(per_page)
-      when 'milestones'
-        milestones.page(page).per(per_page)
-      else
-        Kaminari.paginate_array([]).page(page).per(per_page)
-      end
+    def objects(scope, page = nil, without_count = true)
+      collection = case scope
+                   when 'projects'
+                     projects.page(page).per(per_page)
+                   when 'issues'
+                     issues.page(page).per(per_page)
+                   when 'merge_requests'
+                     merge_requests.page(page).per(per_page)
+                   when 'milestones'
+                     milestones.page(page).per(per_page)
+                   else
+                     Kaminari.paginate_array([]).page(page).per(per_page)
+                   end
+
+      without_count ? collection.without_count : collection
     end
 
     def projects_count
@@ -71,18 +73,46 @@ module Gitlab
       @milestones_count ||= milestones.count
     end
 
+    def limited_projects_count
+      @limited_projects_count ||= projects.limit(count_limit).count
+    end
+
+    def limited_issues_count
+      return @limited_issues_count if @limited_issues_count
+
+      # By default getting limited count (e.g. 1000+) is fast on issuable
+      # collections except for issues, where filtering both not confidential
+      # and confidential issues user has access to, is too complex.
+      # It's faster to try to fetch all public issues first, then only
+      # if necessary try to fetch all issues.
+      sum = issues(public_only: true).limit(count_limit).count
+      @limited_issues_count = sum < count_limit ? issues.limit(count_limit).count : sum
+    end
+
+    def limited_merge_requests_count
+      @limited_merge_requests_count ||= merge_requests.limit(count_limit).count
+    end
+
+    def limited_milestones_count
+      @limited_milestones_count ||= milestones.limit(count_limit).count
+    end
+
     def single_commit_result?
       false
     end
 
+    def count_limit
+      1001
+    end
+
     private
 
     def projects
       limit_projects.search(query)
     end
 
-    def issues
-      issues = IssuesFinder.new(current_user).execute
+    def issues(finder_params = {})
+      issues = IssuesFinder.new(current_user, finder_params).execute
       unless default_project_filter
         issues = issues.where(project_id: project_ids_relation)
       end
@@ -94,13 +124,13 @@ module Gitlab
           issues.full_search(query)
         end
 
-      issues.order('updated_at DESC')
+      issues.reorder('updated_at DESC')
     end
 
     def milestones
       milestones = Milestone.where(project_id: project_ids_relation)
       milestones = milestones.search(query)
-      milestones.order('updated_at DESC')
+      milestones.reorder('updated_at DESC')
     end
 
     def merge_requests
@@ -116,7 +146,7 @@ module Gitlab
           merge_requests.full_search(query)
         end
 
-      merge_requests.order('updated_at DESC')
+      merge_requests.reorder('updated_at DESC')
     end
 
     def default_scope

lib/gitlab/snippet_search_results.rb

@@ -16,7 +16,7 @@ module Gitlab
       when 'snippet_blobs'
         snippet_blobs.page(page).per(per_page)
       else
-        super
+        super(scope, nil, false)
       end
     end
 

spec/features/global_search_spec.rb

@@ -22,7 +22,7 @@ feature 'Global search' do
       click_button "Go"
 
       select_filter("Issues")
-      expect(page).to have_selector('.gl-pagination .page', count: 2)
+      expect(page).to have_selector('.gl-pagination .next')
     end
   end
 end

spec/lib/gitlab/search_results_spec.rb

@@ -19,6 +19,12 @@ describe Gitlab::SearchResults do
       project.add_developer(user)
     end
 
+    describe '#objects' do
+      it 'returns without_page collection by default' do
+        expect(results.objects('projects')).to be_kind_of(Kaminari::PaginatableWithoutCount)
+      end
+    end
+
     describe '#projects_count' do
       it 'returns the total amount of projects' do
         expect(results.projects_count).to eq(1)
@@ -43,6 +49,58 @@ describe Gitlab::SearchResults do
       end
     end
 
+    context "when count_limit is lower than total amount" do
+      before do
+        allow(results).to receive(:count_limit).and_return(1)
+      end
+
+      describe '#limited_projects_count' do
+        it 'returns the limited amount of projects' do
+          create(:project, name: 'foo2')
+
+          expect(results.limited_projects_count).to eq(1)
+        end
+      end
+
+      describe '#limited_merge_requests_count' do
+        it 'returns the limited amount of merge requests' do
+          create(:merge_request, :simple, source_project: project, title: 'foo2')
+
+          expect(results.limited_merge_requests_count).to eq(1)
+        end
+      end
+
+      describe '#limited_milestones_count' do
+        it 'returns the limited amount of milestones' do
+          create(:milestone, project: project, title: 'foo2')
+
+          expect(results.limited_milestones_count).to eq(1)
+        end
+      end
+
+      describe '#limited_issues_count' do
+        it 'runs single SQL query to get the limited amount of issues' do
+          create(:milestone, project: project, title: 'foo2')
+
+          expect(results).to receive(:issues).with(public_only: true).and_call_original
+          expect(results).not_to receive(:issues).with(no_args).and_call_original
+
+          expect(results.limited_issues_count).to eq(1)
+        end
+      end
+    end
+
+    context "when count_limit is higher than total amount" do
+      describe '#limited_issues_count' do
+        it 'runs multiple queries to get the limited amount of issues' do
+          expect(results).to receive(:issues).with(public_only: true).and_call_original
+          expect(results).to receive(:issues).with(no_args).and_call_original
+
+          expect(results.limited_issues_count).to eq(1)
+        end
+      end
+    end
+
     it 'includes merge requests from source and target projects' do
       forked_project = fork_project(project, user)
       merge_request_2 = create(:merge_request, target_project: project, source_project: forked_project, title: 'foo')