Cache the commit author in RequestStore to avoid extra lookups in PostReceive

In a PostReceive task with 697 commits (8.9 RC1 -> RC8), looking up the commit author takes about 10% of the time. Caching this information in RequestStore saves a few seconds from the overall processing time.

Improves #18663 (moved)

app/models/commit.rb

@@ -178,7 +178,18 @@ class Commit
   end
   def author
-    @author ||= User.find_by_any_email(author_email.downcase)
+    if RequestStore.active?
+      key = "commit_author:#{author_email.downcase}"
+      # nil is a valid value since no author may exist in the system
+      if RequestStore.store.has_key?(key)
+        @author = RequestStore.store[key]
+      else
+        @author = find_author_by_any_email
+        RequestStore.store[key] = @author
+      end
+    else
+      @author ||= find_author_by_any_email
+    end
   end
   def committer
@@ -306,6 +317,10 @@ class Commit
   private
+  def find_author_by_any_email
+    User.find_by_any_email(author_email.downcase)
+  end
+
   def repo_changes
     changes = { added: [], modified: [], removed: [] }

[yorickpeterse-staging]

@stanhu Doesn't @author = RequestStore.store[key] ||= find_author_by_any_email work just as well (while being less verbose)?

[Stan Hu]

I originally had that, but then changed it because:

1. find_author_by_any_email can return nil, so I found that if the user were missing we would continue to do lookups
2. Specs failed since RequestStore would store stale data

[yorickpeterse-staging]

@stanhu Ah, gotcha.