Memoize MR merged/closed events retrieval

CHANGELOG

@@ -45,6 +45,7 @@ v 8.10.0 (unreleased)
   - RailsCache metris now includes fetch_hit/fetch_miss and read_hit/read_miss info.
   - Allow [ci skip] to be in any case and allow [skip ci]. !4785 (simon_w)
   - Set import_url validation to be more strict
+  - Memoize MR merged/closed events retrieval
   - Add basic system information like memory and disk usage to the admin panel
   - Don't garbage collect commits that have related DB records like comments
   - More descriptive message for git hooks and file locks

app/models/merge_request.rb

@@ -318,11 +318,11 @@ class MergeRequest < ActiveRecord::Base
   end
 
   def merge_event
-    self.target_project.events.where(target_id: self.id, target_type: "MergeRequest", action: Event::MERGED).last
+    @merge_event ||= target_project.events.where(target_id: self.id, target_type: "MergeRequest", action: Event::MERGED).last
   end
 
   def closed_event
-    self.target_project.events.where(target_id: self.id, target_type: "MergeRequest", action: Event::CLOSED).last
+    @closed_event ||= target_project.events.where(target_id: self.id, target_type: "MergeRequest", action: Event::CLOSED).last
   end
 
   WIP_REGEX = /\A\s*(\[WIP\]\s*|WIP:\s*|WIP\s+)+\s*/i.freeze