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.

3 files changed, 32 insertions, 6 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] }