Fix N+1 queries with loading group issues with GraphQL

Previously when group issues were queried, we called a SELECT for each
project and its associated project features to check whether the user
had permission to read the issue. We now solve this by preloading those
items unconditionally.

app/graphql/resolvers/issues_resolver.rb

@@ -19,7 +19,7 @@ module Resolvers
                                  milestone_due_asc milestone_due_desc].freeze
 
     def continue_issue_resolve(parent, finder, **args)
-      issues = apply_lookahead(Gitlab::Graphql::Loaders::IssuableLoader.new(parent, finder).batching_find_all)
+      issues = Gitlab::Graphql::Loaders::IssuableLoader.new(parent, finder).batching_find_all { |q| apply_lookahead(q) }
 
       if non_stable_cursor_sort?(args[:sort])
         # Certain complex sorts are not supported by the stable cursor pagination yet.
@@ -32,6 +32,14 @@ module Resolvers
 
     private
 
+    def unconditional_includes
+      [
+        {
+          project: [:project_feature]
+        }
+      ]
+    end
+
     def preloads
       {
         alert_management_alert: [:alert_management_alert],

changelogs/unreleased/sh-fix-nplus-one-graphql-group-issues.yml

+---
+title: Fix N+1 queries with loading group issues with GraphQL
+merge_request: 50328
+author:
+type: performance

ee/spec/graphql/types/issue_type_spec.rb

@@ -23,14 +23,19 @@ RSpec.describe GitlabSchema.types['Issue'] do
 
     shared_examples 'avoids N+1 queries on blocked' do
       specify do
+        # Warm up table schema and other data (e.g. SAML providers, license)
+        GitlabSchema.execute(query, context: { current_user: user })
+
         control_count = ActiveRecord::QueryRecorder.new { GitlabSchema.execute(query, context: { current_user: user }) }.count
 
         blocked_issue2 = create(:issue, project: project)
         blocking_issue2 = create(:issue, project: project)
         create :issue_link, source: blocked_issue2, target: blocking_issue2, link_type: IssueLink::TYPE_IS_BLOCKED_BY
 
-        # added the +1 due to an existing N+1 with issues
-        expect { GitlabSchema.execute(query, context: { current_user: user }) }.not_to exceed_query_limit(control_count + 1)
+        project2 = create(:project, :public, group: group)
+        create(:issue, project: project2)
+
+        expect { GitlabSchema.execute(query, context: { current_user: user }) }.not_to exceed_query_limit(control_count)
       end
     end
 

spec/graphql/resolvers/issues_resolver_spec.rb

@@ -264,13 +264,13 @@ RSpec.describe Resolvers::IssuesResolver do
       end
 
       it 'finds a specific issue with iid', :request_store do
-        result = batch_sync(max_queries: 2) { resolve_issues(iid: issue1.iid) }
+        result = batch_sync(max_queries: 4) { resolve_issues(iid: issue1.iid) }
 
         expect(result).to contain_exactly(issue1)
       end
 
       it 'batches queries that only include IIDs', :request_store do
-        result = batch_sync(max_queries: 2) do
+        result = batch_sync(max_queries: 4) do
           [issue1, issue2]
             .map { |issue| resolve_issues(iid: issue.iid.to_s) }
             .flat_map(&:to_a)
@@ -280,7 +280,7 @@ RSpec.describe Resolvers::IssuesResolver do
       end
 
       it 'finds a specific issue with iids', :request_store do
-        result = batch_sync(max_queries: 2) do
+        result = batch_sync(max_queries: 4) do
           resolve_issues(iids: [issue1.iid])
         end