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, 20 insertions, 1 deletions

diff --git a/lib/gitlab/gitaly_client.rb b/lib/gitlab/gitaly_client.rb
index e3b9a7a1a89..bc2f7693fdc 100644
--- a/lib/gitlab/gitaly_client.rb
+++ b/lib/gitlab/gitaly_client.rb
@@ -296,6 +296,25 @@ module Gitlab
       end
     end
 
+    # Normally a FindCommit RPC will cache the commit with its SHA
+    # instead of a ref name, since it's possible the branch is mutated
+    # afterwards. However, for read-only requests that never mutate the
+    # branch, this method allows caching of the ref name directly.
+    def self.allow_ref_name_caching
+      return yield unless Gitlab::SafeRequestStore.active?
+
+      begin
+        Gitlab::SafeRequestStore[:allow_ref_name_caching] = true
+        yield
+      ensure
+        Gitlab::SafeRequestStore[:allow_ref_name_caching] = false
+      end
+    end
+
+    def self.ref_name_caching_allowed?
+      Gitlab::SafeRequestStore[:allow_ref_name_caching]
+    end
+
     def self.get_call_count(key)
       Gitlab::SafeRequestStore[key] || 0
     end
diff --git a/lib/gitlab/gitaly_client/commit_service.rb b/lib/gitlab/gitaly_client/commit_service.rb
index ea12424eb4a..0d5debfcd01 100644
--- a/lib/gitlab/gitaly_client/commit_service.rb
+++ b/lib/gitlab/gitaly_client/commit_service.rb
@@ -286,7 +286,7 @@ module Gitlab
           commit = call_find_commit(revision)
           return unless commit
 
-          key[:commit_id] = commit.id
+          key[:commit_id] = commit.id unless GitalyClient.ref_name_caching_allowed?
           Gitlab::SafeRequestStore[key] = commit
         else
           call_find_commit(revision)