Re-use issue/MR counts for the pagination systemmr-index-page-performance

This changes the issue and MR index pages so the pagination system
re-uses the output of the COUNT(*) query used to calculate the number of
rows per state (opened, closed, etc). This removes the need for an
additional COUNT(*) on both pages.

7 files changed, 40 insertions, 9 deletions

diff --git a/app/controllers/concerns/issuable_collections.rb b/app/controllers/concerns/issuable_collections.rb
index a34a82b7ba6..23909bd2d39 100644
--- a/app/controllers/concerns/issuable_collections.rb
+++ b/app/controllers/concerns/issuable_collections.rb
@@ -36,6 +36,34 @@ module IssuableCollections
     @merge_requests_finder ||= issuable_finder_for(MergeRequestsFinder)
   end
 
+  def redirect_out_of_range(relation, total_pages)
+    return false if total_pages.zero?
+
+    out_of_range = relation.current_page > total_pages
+
+    if out_of_range
+      redirect_to(url_for(params.merge(page: total_pages, only_path: true)))
+    end
+
+    out_of_range
+  end
+
+  def issues_page_count(relation)
+    page_count_for_relation(relation, issues_finder.row_count)
+  end
+
+  def merge_requests_page_count(relation)
+    page_count_for_relation(relation, merge_requests_finder.row_count)
+  end
+
+  def page_count_for_relation(relation, row_count)
+    limit = relation.limit_value.to_f
+
+    return 1 if limit.zero?
+
+    (row_count.to_f / limit).ceil
+  end
+
   def issuable_finder_for(finder_class)
     finder_class.new(current_user, filter_params)
   end
diff --git a/app/controllers/projects/issues_controller.rb b/app/controllers/projects/issues_controller.rb
index 0d4266f0899..dc9e6f71152 100644
--- a/app/controllers/projects/issues_controller.rb
+++ b/app/controllers/projects/issues_controller.rb
@@ -27,10 +27,9 @@ class Projects::IssuesController < Projects::ApplicationController
     @issues             = issues_collection
     @issues             = @issues.page(params[:page])
     @issuable_meta_data = issuable_meta_data(@issues, @collection_type)
+    @total_pages        = issues_page_count(@issues)
 
-    if @issues.out_of_range? && @issues.total_pages != 0
-      return redirect_to url_for(params.merge(page: @issues.total_pages, only_path: true))
-    end
+    return if redirect_out_of_range(@issues, @total_pages)
 
     if params[:label_name].present?
       @labels = LabelsFinder.new(current_user, project_id: @project.id, title: params[:label_name]).execute
diff --git a/app/controllers/projects/merge_requests_controller.rb b/app/controllers/projects/merge_requests_controller.rb
index e3fa3736808..5095d7fd445 100644
--- a/app/controllers/projects/merge_requests_controller.rb
+++ b/app/controllers/projects/merge_requests_controller.rb
@@ -18,10 +18,9 @@ class Projects::MergeRequestsController < Projects::MergeRequests::ApplicationCo
     @merge_requests     = @merge_requests.page(params[:page])
     @merge_requests     = @merge_requests.preload(merge_request_diff: :merge_request)
     @issuable_meta_data = issuable_meta_data(@merge_requests, @collection_type)
+    @total_pages        = merge_requests_page_count(@merge_requests)
 
-    if @merge_requests.out_of_range? && @merge_requests.total_pages != 0
-      return redirect_to url_for(params.merge(page: @merge_requests.total_pages, only_path: true))
-    end
+    return if redirect_out_of_range(@merge_requests, @total_pages)
 
     if params[:label_name].present?
       labels_params = { project_id: @project.id, title: params[:label_name] }
diff --git a/app/finders/issuable_finder.rb b/app/finders/issuable_finder.rb
index c8dd2275730..9848497f258 100644
--- a/app/finders/issuable_finder.rb
+++ b/app/finders/issuable_finder.rb
@@ -61,6 +61,10 @@ class IssuableFinder
     execute.find_by(*params)
   end
 
+  def row_count
+    Gitlab::IssuablesCountForState.new(self).for_state_or_opened(params[:state])
+  end
+
   # We often get counts for each state by running a query per state, and
   # counting those results. This is typically slower than running one query
   # (even if that query is slower than any of the individual state queries) and
diff --git a/app/helpers/issuables_helper.rb b/app/helpers/issuables_helper.rb
index 681615dbf3e..717abf2082d 100644
--- a/app/helpers/issuables_helper.rb
+++ b/app/helpers/issuables_helper.rb
@@ -240,7 +240,8 @@ module IssuablesHelper
 
   def issuables_count_for_state(issuable_type, state)
     finder = public_send("#{issuable_type}_finder") # rubocop:disable GitlabSecurity/PublicSend
-    finder.count_by_state[state]
+
+    Gitlab::IssuablesCountForState.new(finder)[state]
   end
 
   def close_issuable_url(issuable)
diff --git a/app/views/projects/issues/_issues.html.haml b/app/views/projects/issues/_issues.html.haml
index 34d5a3e1831..6fb5aa45166 100644
--- a/app/views/projects/issues/_issues.html.haml
+++ b/app/views/projects/issues/_issues.html.haml
@@ -4,4 +4,4 @@
     = render 'shared/empty_states/issues'
 
 - if @issues.present?
-  = paginate @issues, theme: "gitlab"
+  = paginate @issues, theme: "gitlab", total_pages: @total_pages
diff --git a/app/views/projects/merge_requests/_merge_requests.html.haml b/app/views/projects/merge_requests/_merge_requests.html.haml
index 4e97f74dd6a..bd6f1c05949 100644
--- a/app/views/projects/merge_requests/_merge_requests.html.haml
+++ b/app/views/projects/merge_requests/_merge_requests.html.haml
@@ -5,4 +5,4 @@
     = render 'shared/empty_states/merge_requests'
 
 - if @merge_requests.present?
-  = paginate @merge_requests, theme: "gitlab"
+  = paginate @merge_requests, theme: "gitlab", total_pages: @total_pages