Only expire tag cache once per push

Previously each tag in a push would invoke the Gitaly `FindAllTags` RPC
since the tag cache would be invalidated with every tag.

We can eliminate those extraneous calls by expiring the tag cache once
in `PostReceive` and taking advantage of the cached tags.

Relates to https://gitlab.com/gitlab-org/gitlab-ce/issues/65795

app/models/repository.rb

@@ -418,25 +418,29 @@ class Repository
   end
 
   # Runs code before pushing (= creating or removing) a tag.
+  #
+  # Note that this doesn't expire the tags. You may need to call
+  # expire_caches_for_tags or expire_tags_cache.
   def before_push_tag
+    repository_event(:push_tag)
+  end
+
+  def expire_caches_for_tags
     expire_statistics_caches
     expire_emptiness_caches
     expire_tags_cache
-
-    repository_event(:push_tag)
   end
 
   # Runs code before removing a tag.
   def before_remove_tag
-    expire_tags_cache
-    expire_statistics_caches
+    expire_caches_for_tags
 
     repository_event(:remove_tag)
   end
 
   # Runs code after removing a tag.
   def after_remove_tag
-    expire_tags_cache
+    expire_caches_for_tags
   end
 
   # Runs code after the HEAD of a repository is changed.

app/workers/post_receive.rb

@@ -44,6 +44,8 @@ class PostReceive
 
     # Expire the branches cache so we have updated data for this push
     post_received.project.repository.expire_branches_cache if post_received.includes_branches?
+    # We only need to expire tags once per push
+    post_received.project.repository.expire_caches_for_tags if post_received.includes_tags?
 
     post_received.enum_for(:changes_refs).with_index do |(oldrev, newrev, ref), index|
       service_klass =

changelogs/unreleased/sh-only-flush-tags-once-per-push.yml

@@ -0,0 +1,5 @@
+---
+title: Only expire tag cache once per push
+merge_request: 31641
+author:
+type: performance

lib/gitlab/git_post_receive.rb

@@ -33,6 +33,12 @@ module Gitlab
       end
     end
 
+    def includes_tags?
+      enum_for(:changes_refs).any? do |_oldrev, _newrev, ref|
+        Gitlab::Git.tag_ref?(ref)
+      end
+    end
+
     private
 
     def deserialize_changes(changes)

spec/lib/gitlab/git_post_receive_spec.rb

@@ -49,4 +49,47 @@ describe ::Gitlab::GitPostReceive do
       end
     end
   end
+
+  describe '#includes_tags?' do
+    context 'with no tags' do
+      let(:changes) do
+        <<~EOF
+          654321 210987 refs/notags/tag1
+          654322 210986 refs/heads/test1
+          654323 210985 refs/merge-requests/mr1
+        EOF
+      end
+
+      it 'returns false' do
+        expect(subject.includes_tags?).to be_falsey
+      end
+    end
+
+    context 'with tags' do
+      let(:changes) do
+        <<~EOF
+          654322 210986 refs/heads/test1
+          654321 210987 refs/tags/tag1
+          654323 210985 refs/merge-requests/mr1
+        EOF
+      end
+
+      it 'returns true' do
+        expect(subject.includes_tags?).to be_truthy
+      end
+    end
+
+    context 'with malformed changes' do
+      let(:changes) do
+        <<~EOF
+          ref/tags/1 a
+          sometag refs/tags/2
+        EOF
+      end
+
+      it 'returns false' do
+        expect(subject.includes_tags?).to be_falsey
+      end
+    end
+  end
 end

spec/models/repository_spec.rb

@@ -1744,12 +1744,23 @@ describe Repository do
     end
   end
 
-  describe '#before_push_tag' do
+  describe '#expires_caches_for_tags' do
     it 'flushes the cache' do
       expect(repository).to receive(:expire_statistics_caches)
       expect(repository).to receive(:expire_emptiness_caches)
       expect(repository).to receive(:expire_tags_cache)
 
+      repository.expire_caches_for_tags
+    end
+  end
+
+  describe '#before_push_tag' do
+    it 'logs an event' do
+      expect(repository).not_to receive(:expire_statistics_caches)
+      expect(repository).not_to receive(:expire_emptiness_caches)
+      expect(repository).not_to receive(:expire_tags_cache)
+      expect(repository).to receive(:repository_event).with(:push_tag)
+
       repository.before_push_tag
     end
   end

spec/services/git/tag_push_service_spec.rb

@@ -26,8 +26,8 @@ describe Git::TagPushService do
       subject
     end
 
-    it 'flushes the tags cache' do
-      expect(project.repository).to receive(:expire_tags_cache)
+    it 'does not flush the tags cache' do
+      expect(project.repository).not_to receive(:expire_tags_cache)
 
       subject
     end

spec/workers/post_receive_spec.rb

@@ -85,8 +85,20 @@ describe PostReceive do
         end
       end
 
-      context 'tags' do
-        let(:changes) { '123456 789012 refs/tags/tag' }
+      context "tags" do
+        let(:changes) do
+          <<~EOF
+            654321 210987 refs/tags/tag1
+            654322 210986 refs/tags/tag2
+            654323 210985 refs/tags/tag3
+            654324 210984 refs/tags/tag4
+            654325 210983 refs/tags/tag5
+          EOF
+        end
+
+        before do
+          expect(Gitlab::GlRepository).to receive(:parse).and_return([project, Gitlab::GlRepository::PROJECT])
+        end
 
         it 'does not expire branches cache' do
           expect(project.repository).not_to receive(:expire_branches_cache)
@@ -94,8 +106,18 @@ describe PostReceive do
           described_class.new.perform(gl_repository, key_id, base64_changes)
         end
 
-        it 'calls Git::TagPushService' do
-          expect_next_instance_of(Git::TagPushService) do |service|
+        it "only invalidates tags once" do
+          expect(project.repository).to receive(:repository_event).exactly(5).times.with(:push_tag).and_call_original
+          expect(project.repository).to receive(:expire_caches_for_tags).once.and_call_original
+          expect(project.repository).to receive(:expire_tags_cache).once.and_call_original
+
+          described_class.new.perform(gl_repository, key_id, base64_changes)
+        end
+
+        it "calls Git::TagPushService" do
+          expect(Git::BranchPushService).not_to receive(:new)
+
+          expect_any_instance_of(Git::TagPushService) do |service|
             expect(service).to receive(:execute).and_return(true)
           end