Speed up pull mirroring by asking Gitaly if tags have changed

Currently, pull mirroring will fetch the full list of tags for a
repository twice - before and after the pull - and use the diff between
them to work out which new tags have been added.

This seems unavoidable with the current output of `git fetch`, but we
*can* skip doing the second call (and cache invalidation) if there have
been no tag changes. This is the common, happy path, so should be worth
implementing.

Gemfile

@@ -465,7 +465,7 @@ group :ed25519 do
 end
 
 # Gitaly GRPC protocol definitions
-gem 'gitaly', '~> 13.7.0.pre.rc1'
+gem 'gitaly', '~> 13.8.0.pre.rc2'
 
 gem 'grpc', '~> 1.30.2'
 

Gemfile.lock

@@ -417,7 +417,7 @@ GEM
       rails (>= 3.2.0)
     git (1.7.0)
       rchardet (~> 1.8)
-    gitaly (13.7.0.pre.rc1)
+    gitaly (13.8.0.pre.rc2)
       grpc (~> 1.0)
     github-markup (1.7.0)
     gitlab-chronic (0.10.5)
@@ -1358,7 +1358,7 @@ DEPENDENCIES
   gettext (~> 3.3)
   gettext_i18n_rails (~> 1.8.0)
   gettext_i18n_rails_js (~> 1.3)
-  gitaly (~> 13.7.0.pre.rc1)
+  gitaly (~> 13.8.0.pre.rc2)
   github-markup (~> 1.7.0)
   gitlab-chronic (~> 0.10.5)
   gitlab-experiment (~> 0.4.5)

ee/app/models/ee/project.rb

@@ -297,7 +297,7 @@ module EE
       mirror? && !empty_repo?
     end
 
-    def fetch_mirror(forced: false)
+    def fetch_mirror(forced: false, check_tags_changed: false)
       return unless mirror?
 
       # Only send the password if it's needed
@@ -308,7 +308,7 @@ module EE
           username_only_import_url
         end
 
-      repository.fetch_upstream(url, forced: forced)
+      repository.fetch_upstream(url, forced: forced, check_tags_changed: check_tags_changed)
     end
 
     def can_override_approvers?

ee/app/models/ee/repository.rb

@@ -33,9 +33,10 @@ module EE
       expire_content_cache
     end
 
-    def fetch_upstream(url, forced: false)
+    def fetch_upstream(url, forced: false, check_tags_changed: false)
       add_remote(MIRROR_REMOTE, url)
-      fetch_remote(MIRROR_REMOTE, ssh_auth: project&.import_data, forced: forced)
+
+      fetch_remote(MIRROR_REMOTE, ssh_auth: project&.import_data, forced: forced, check_tags_changed: check_tags_changed)
     end
 
     def upstream_branches

ee/app/services/projects/update_mirror_service.rb

@@ -33,7 +33,7 @@ module Projects
       checksum_before = project.repository.checksum
 
       update_tags do
-        project.fetch_mirror(forced: true)
+        project.fetch_mirror(forced: true, check_tags_changed: Feature.enabled?(:fetch_mirror_check_tags_changed, project))
       end
 
       update_branches
@@ -99,7 +99,7 @@ module Projects
       old_tags = repository_tags_with_target.each_with_object({}) { |tag, tags| tags[tag.name] = tag }
 
       fetch_result = yield
-      return fetch_result unless fetch_result
+      return fetch_result unless fetch_result&.tags_changed
 
       repository.expire_tags_cache
 

ee/config/feature_flags/development/fetch_mirror_check_tags_changed.yml

+---
+name: fetch_mirror_check_tags_changed
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/49629
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/292602
+milestone: '13.8'
+type: development
+group: group::source code
+default_enabled: false

ee/spec/models/project_spec.rb

@@ -896,7 +896,7 @@ RSpec.describe Project do
       let(:project) { build(:project, :mirror, import_url: import_url, import_data_attributes: { auth_method: auth_method } ) }
 
       specify do
-        expect(project.repository).to receive(:fetch_upstream).with(expected, forced: false)
+        expect(project.repository).to receive(:fetch_upstream).with(expected, forced: false, check_tags_changed: false)
 
         project.fetch_mirror
       end

ee/spec/services/projects/update_mirror_service_spec.rb

@@ -100,14 +100,24 @@ RSpec.describe Projects::UpdateMirrorService do
     end
 
     context "updating tags" do
-      it "creates new tags" do
+      it "creates new tags, expiring cache if there are tag changes" do
         stub_fetch_mirror(project)
 
+        expect(project.repository).to receive(:expire_tags_cache).and_call_original
+
         service.execute
 
         expect(project.repository.tag_names).to include('new-tag')
       end
 
+      it 'does not expire cache if there are no tag changes' do
+        stub_fetch_mirror(project, tags_changed: false)
+
+        expect(project.repository).not_to receive(:expire_tags_cache)
+
+        service.execute
+      end
+
       it "only invokes Git::TagPushService for tags pointing to commits" do
         stub_fetch_mirror(project)
 
@@ -429,11 +439,11 @@ RSpec.describe Projects::UpdateMirrorService do
     end
   end
 
-  def stub_fetch_mirror(project, repository: project.repository)
-    allow(project).to receive(:fetch_mirror) { fetch_mirror(repository) }
+  def stub_fetch_mirror(project, repository: project.repository, tags_changed: true )
+    allow(project).to receive(:fetch_mirror) { fetch_mirror(repository, tags_changed: tags_changed) }
   end
 
-  def fetch_mirror(repository)
+  def fetch_mirror(repository, tags_changed: true)
     rugged = rugged_repo(repository)
     masterrev = repository.find_branch("master").dereferenced_target.id
 
@@ -457,6 +467,8 @@ RSpec.describe Projects::UpdateMirrorService do
 
     # New tag that point to a blob
     rugged.references.create('refs/tags/new-tag-on-blob', 'c74175afd117781cbc983664339a0f599b5bb34e')
+
+    Gitaly::FetchRemoteResponse.new(tags_changed: tags_changed)
   end
 
   def modify_tag(repository, tag_name)

lib/gitlab/git/repository.rb

@@ -801,7 +801,8 @@ module Gitlab
       # forced - should we use --force flag?
       # no_tags - should we use --no-tags flag?
       # prune - should we use --prune flag?
-      def fetch_remote(remote, ssh_auth: nil, forced: false, no_tags: false, prune: true)
+      # check_tags_changed - should we ask gitaly to calculate whether any tags changed?
+      def fetch_remote(remote, ssh_auth: nil, forced: false, no_tags: false, prune: true, check_tags_changed: false)
         wrapped_gitaly_errors do
           gitaly_repository_client.fetch_remote(
             remote,
@@ -809,6 +810,7 @@ module Gitlab
             forced: forced,
             no_tags: no_tags,
             prune: prune,
+            check_tags_changed: check_tags_changed,
             timeout: GITLAB_PROJECTS_TIMEOUT
           )
         end

lib/gitlab/gitaly_client/repository_service.rb

@@ -70,10 +70,11 @@ module Gitlab
         end.join
       end
 
-      def fetch_remote(remote, ssh_auth:, forced:, no_tags:, timeout:, prune: true)
+      def fetch_remote(remote, ssh_auth:, forced:, no_tags:, timeout:, prune: true, check_tags_changed: false)
         request = Gitaly::FetchRemoteRequest.new(
           repository: @gitaly_repo, remote: remote, force: forced,
-          no_tags: no_tags, timeout: timeout, no_prune: !prune
+          no_tags: no_tags, timeout: timeout, no_prune: !prune,
+          check_tags_changed: check_tags_changed
         )
 
         if ssh_auth&.ssh_mirror_url?

spec/lib/gitlab/git/repository_spec.rb

@@ -520,12 +520,13 @@ RSpec.describe Gitlab::Git::Repository, :seed_helper do
         forced: true,
         no_tags: true,
         timeout: described_class::GITLAB_PROJECTS_TIMEOUT,
-        prune: false
+        prune: false,
+        check_tags_changed: false
       }
 
       expect(repository.gitaly_repository_client).to receive(:fetch_remote).with('remote-name', expected_opts)
 
-      repository.fetch_remote('remote-name', ssh_auth: ssh_auth, forced: true, no_tags: true, prune: false)
+      repository.fetch_remote('remote-name', ssh_auth: ssh_auth, forced: true, no_tags: true, prune: false, check_tags_changed: false)
     end
 
     it_behaves_like 'wrapping gRPC errors', Gitlab::GitalyClient::RepositoryService, :fetch_remote do

spec/lib/gitlab/gitaly_client/repository_service_spec.rb

@@ -131,7 +131,8 @@ RSpec.describe Gitlab::GitalyClient::RepositoryService do
         known_hosts: '',
         force: false,
         no_tags: false,
-        no_prune: false
+        no_prune: false,
+        check_tags_changed: false
       )
 
       expect_any_instance_of(Gitaly::RepositoryService::Stub)
@@ -139,7 +140,7 @@ RSpec.describe Gitlab::GitalyClient::RepositoryService do
         .with(expected_request, kind_of(Hash))
         .and_return(double(value: true))
 
-      client.fetch_remote(remote, ssh_auth: nil, forced: false, no_tags: false, timeout: 1)
+      client.fetch_remote(remote, ssh_auth: nil, forced: false, no_tags: false, timeout: 1, check_tags_changed: false)
     end
 
     context 'SSH auth' do