Optimize maximum user access level lookup in loading of notes

NotesHelper#note_editable? and ProjectTeam#human_max_access currently
take about 16% of the load time of an issue page. This MR preloads
the maximum access level of users for all notes in issues and merge
requests with several queries instead of one per user and caches
the result in RequestStore.

1 files changed, 35 insertions, 11 deletions

diff --git a/app/models/project_team.rb b/app/models/project_team.rb
index 9d312a53790..67faea1f9f3 100644
--- a/app/models/project_team.rb
+++ b/app/models/project_team.rb
@@ -132,22 +132,41 @@ class ProjectTeam
     Gitlab::Access.options_with_owner.key(max_member_access(user_id))
   end
 
-  # This method assumes project and group members are eager loaded for optimal
-  # performance.
-  def max_member_access(user_id)
-    access = []
+  # Determine the maximum access level for a group of users in bulk.
+  #
+  # Returns a Hash mapping user ID -> maxmum access level.
+  def max_member_access_for_user_ids(user_ids)
+    user_ids = user_ids.uniq
+    key = "max_member_access:#{project.id}"
+    RequestStore.store[key] ||= Hash.new
+    access = RequestStore.store[key]
 
-    access += project.members.where(user_id: user_id).has_access.pluck(:access_level)
+    # Lookup only the IDs we need
+    user_ids = user_ids - access.keys
 
-    if group
-      access += group.members.where(user_id: user_id).has_access.pluck(:access_level)
-    end
+    if user_ids.present?
+      user_ids.map { |id| access[id] = Gitlab::Access::NO_ACCESS }
 
-    if project.invited_groups.any? && project.allowed_to_share_with_group?
-      access << max_invited_level(user_id)
+      member_access = project.members.where(user_id: user_ids).has_access.pluck(:user_id, :access_level).to_h
+      merge_max!(access, member_access)
+
+      if group
+        group_access = group.members.where(user_id: user_ids).has_access.pluck(:user_id, :access_level).to_h
+        merge_max!(access, group_access)
+      end
+
+      if project.invited_groups.any? && project.allowed_to_share_with_group?
+        # Not optimized
+        invited_levels = user_ids.map { |id| [id, max_invited_level(id)] }.to_h
+        merge_max!(access, invited_levels)
+      end
     end
 
-    access.compact.max
+    access
+  end
+
+  def max_member_access(user_id)
+    max_member_access_for_user_ids([user_id])[user_id]
   end
 
   private
@@ -156,6 +175,7 @@ class ProjectTeam
     project.project_group_links.map do |group_link|
       invited_group = group_link.group
       access = invited_group.group_members.find_by(user_id: user_id).try(:access_field)
+      access = Gitlab::Access::NO_ACCESS unless access.present?
 
       # If group member has higher access level we should restrict it
       # to max allowed access level
@@ -215,4 +235,8 @@ class ProjectTeam
   def group
     project.group
   end
+
+  def merge_max!(first_hash, second_hash)
+    first_hash.merge!(second_hash) { |_key, old, new| old > new ? old : new }
+  end
 end