Allow ref name caching CommitService#find_commit

For a given merge request, it's quite common to see duplicate FindCommit
Gitaly requests because the Gitaly CommitService caches the request by
the commit SHA, not by the ref name. However, most of the duplicate
requests use the ref name, so the cache is never actually used in
practice. This leads to unnecessary requests that slow performance.

This commit allows certain callers to bypass the ref name to
OID conversion in the cache. We don't do this by default because it's
possible the tip of the branch changes during the commit, which
would cause the caller to get stale data.

This commit also forces the Ci::Pipeline to use the full ref name
so that caching can work for merge requests.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/57083

2 files changed, 17 insertions, 13 deletions

diff --git a/app/controllers/projects/merge_requests_controller.rb b/app/controllers/projects/merge_requests_controller.rb
index 5cf7fa3422d..34cb0416965 100644
--- a/app/controllers/projects/merge_requests_controller.rb
+++ b/app/controllers/projects/merge_requests_controller.rb
@@ -315,7 +315,9 @@ class Projects::MergeRequestsController < Projects::MergeRequests::ApplicationCo
   end
 
   def serializer
-    MergeRequestSerializer.new(current_user: current_user, project: merge_request.project)
+    ::Gitlab::GitalyClient.allow_ref_name_caching do
+      MergeRequestSerializer.new(current_user: current_user, project: merge_request.project)
+    end
   end
 
   def define_edit_vars
diff --git a/app/models/ci/pipeline.rb b/app/models/ci/pipeline.rb
index 826b3f82bbf..bbde0cdd465 100644
--- a/app/models/ci/pipeline.rb
+++ b/app/models/ci/pipeline.rb
@@ -465,9 +465,9 @@ module Ci
     end
 
     def latest?
-      return false unless ref && commit.present?
+      return false unless git_ref && commit.present?
 
-      project.commit(ref) == commit
+      project.commit(git_ref) == commit
     end
 
     def retried
@@ -781,16 +781,18 @@ module Ci
     end
 
     def git_ref
-      if merge_request_event?
-        ##
-        # In the future, we're going to change this ref to
-        # merge request's merged reference, such as "refs/merge-requests/:iid/merge".
-        # In order to do that, we have to update GitLab-Runner's source pulling
-        # logic.
-        # See https://gitlab.com/gitlab-org/gitlab-runner/merge_requests/1092
-        Gitlab::Git::BRANCH_REF_PREFIX + ref.to_s
-      else
-        super
+      strong_memoize(:git_pref) do
+        if merge_request_event?
+          ##
+          # In the future, we're going to change this ref to
+          # merge request's merged reference, such as "refs/merge-requests/:iid/merge".
+          # In order to do that, we have to update GitLab-Runner's source pulling
+          # logic.
+          # See https://gitlab.com/gitlab-org/gitlab-runner/merge_requests/1092
+          Gitlab::Git::BRANCH_REF_PREFIX + ref.to_s
+        else
+          super
+        end
       end
     end