Bring back Rugged implementation of find_commit

This brings back some of the changes in
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/20339.

For users using Gitaly on top of NFS, accessing the Git data directly
via Rugged is more performant than Gitaly. This merge request introduces
the feature flag `rugged_find_commit` to activate Rugged paths.

There are also Rake tasks `gitlab:features:enable_rugged` and
`gitlab:features:disable_rugged` to enable/disable these feature
flags altogether.

Part of four Rugged changes identified in
https://gitlab.com/gitlab-org/gitlab-ce/issues/57317.

changelogs/unreleased/sh-rugged-find-commit.yml

+---
+title: Bring back Rugged implementation of find_commit
+merge_request: 25477
+author:
+type: fixed

doc/administration/high_availability/nfs.md

@@ -37,6 +37,28 @@ options:
   circumstances it could lead to data loss if a failure occurs before data has
   synced.
 
+### Improving NFS performance with GitLab
+
+If you are using NFS to share Git data, we recommend that you enable a
+number of feature flags that will allow GitLab application processes to
+access Git data directly instead of going through the [Gitaly
+service](../gitaly/index.md). Depending on your workload and disk
+performance, these flags may help improve performance. See [the
+issue](https://gitlab.com/gitlab-org/gitlab-ce/issues/57317) for more
+details.
+
+To do this, run the Rake task:
+
+```sh
+gitlab-rake gitlab:features:enable_rugged
+```
+
+If you need to undo this setting for some reason, run:
+
+```sh
+gitlab-rake gitlab:features:disable_rugged
+```
+
 ### Known issues
 
 On some customer systems, we have seen NFS clients slow precipitously due to

doc/development/gitaly.md

@@ -56,6 +56,44 @@ If your test-suite is failing with Gitaly issues, as a first step, try running:
 rm -rf tmp/tests/gitaly
 ```
 
+## Legacy Rugged code
+
+While Gitaly can handle all Git access, many of GitLab customers still
+run Gitaly atop NFS. The legacy Rugged implementation for Git calls may
+be faster than the Gitaly RPC due to N+1 Gitaly calls and other
+reasons. See [the
+issue](https://gitlab.com/gitlab-org/gitlab-ce/issues/57317) for more
+details.
+
+Until GitLab has eliminated most of these inefficiencies or the use of
+NFS is discontinued for Git data, Rugged implementations of some of the
+most commonly-used RPCs can be enabled via feature flags:
+
+* `rugged_find_commit`
+* `rugged_get_tree_entries`
+* `rugged_tree_entry`
+* `rugged_commit_is_ancestor`
+
+A convenience Rake task can be used to enable or disable these flags
+all together. To enable:
+
+```sh
+bundle exec rake gitlab:features:enable_rugged
+```
+
+To disable:
+
+```sh
+bundle exec rake gitlab:features:disable_rugged
+```
+
+Most of this code exists in the `lib/gitlab/git/rugged_impl` directory.
+
+NOTE: **Note:** You should NOT need to add or modify code related to
+Rugged unless explicitly discussed with the [Gitaly
+Team](https://gitlab.com/groups/gl-gitaly/group_members). This code will
+NOT work on GitLab.com or other GitLab instances that do not use NFS.
+
 ## `TooManyInvocationsError` errors
 
 During development and testing, you may experience `Gitlab::GitalyClient::TooManyInvocationsError` failures.

lib/gitlab/git/commit.rb

@@ -5,6 +5,7 @@ module Gitlab
   module Git
     class Commit
       include Gitlab::EncodingHelper
+      prepend Gitlab::Git::RuggedImpl::Commit
       extend Gitlab::Git::WrapsGitalyErrors
 
       attr_accessor :raw_commit, :head
@@ -62,15 +63,19 @@ module Gitlab
           # This saves us an RPC round trip.
           return nil if commit_id.include?(':')
 
-          commit = wrapped_gitaly_errors do
-            repo.gitaly_commit_client.find_commit(commit_id)
-          end
+          commit = find_commit(repo, commit_id)
 
           decorate(repo, commit) if commit
         rescue Gitlab::Git::CommandError, Gitlab::Git::Repository::NoRepository, ArgumentError
           nil
         end
 
+        def find_commit(repo, commit_id)
+          wrapped_gitaly_errors do
+            repo.gitaly_commit_client.find_commit(commit_id)
+          end
+        end
+
         # Get last commit for HEAD
         #
         # Ex.
@@ -185,6 +190,10 @@ module Gitlab
         @repository = repository
         @head = head
 
+        init_commit(raw_commit)
+      end
+
+      def init_commit(raw_commit)
         case raw_commit
         when Hash
           init_from_hash(raw_commit)
@@ -400,3 +409,5 @@ module Gitlab
     end
   end
 end
+
+Gitlab::Git::Commit.singleton_class.prepend Gitlab::Git::RuggedImpl::Commit::ClassMethods

lib/gitlab/git/ref.rb

@@ -4,6 +4,7 @@ module Gitlab
   module Git
     class Ref
       include Gitlab::EncodingHelper
+      include Gitlab::Git::RuggedImpl::Ref
 
       # Branch or tag name
       # without "refs/tags|heads" prefix

lib/gitlab/git/repository.rb

@@ -11,6 +11,7 @@ module Gitlab
       include Gitlab::Git::WrapsGitalyErrors
       include Gitlab::EncodingHelper
       include Gitlab::Utils::StrongMemoize
+      include Gitlab::Git::RuggedImpl::Repository
 
       SEARCH_CONTEXT_LINES = 3
       REV_LIST_COMMIT_LIMIT = 2_000

lib/gitlab/git/rugged_impl/commit.rb

+# frozen_string_literal: true
+
+# NOTE: This code is legacy. Do not add/modify code here unless you have
+# discussed with the Gitaly team.  See
+# https://docs.gitlab.com/ee/development/gitaly.html#legacy-rugged-code
+# for more details.
+
+# rubocop:disable Gitlab/ModuleWithInstanceVariables
+module Gitlab
+  module Git
+    module RuggedImpl
+      module Commit
+        module ClassMethods
+          extend ::Gitlab::Utils::Override
+
+          def rugged_find(repo, commit_id)
+            obj = repo.rev_parse_target(commit_id)
+
+            obj.is_a?(::Rugged::Commit) ? obj : nil
+          rescue ::Rugged::Error
+            nil
+          end
+
+          override :find_commit
+          def find_commit(repo, commit_id)
+            if Feature.enabled?(:rugged_find_commit)
+              rugged_find(repo, commit_id)
+            else
+              super
+            end
+          end
+        end
+
+        extend ::Gitlab::Utils::Override
+
+        override :init_commit
+        def init_commit(raw_commit)
+          case raw_commit
+          when ::Rugged::Commit
+            init_from_rugged(raw_commit)
+          else
+            super
+          end
+        end
+
+        def init_from_rugged(commit)
+          author = commit.author
+          committer = commit.committer
+
+          @raw_commit = commit
+          @id = commit.oid
+          @message = commit.message
+          @authored_date = author[:time]
+          @committed_date = committer[:time]
+          @author_name = author[:name]
+          @author_email = author[:email]
+          @committer_name = committer[:name]
+          @committer_email = committer[:email]
+          @parent_ids = commit.parents.map(&:oid)
+        end
+      end
+    end
+  end
+end
+# rubocop:enable Gitlab/ModuleWithInstanceVariables

lib/gitlab/git/rugged_impl/ref.rb

+# frozen_string_literal: true
+
+# NOTE: This code is legacy. Do not add/modify code here unless you have
+# discussed with the Gitaly team.  See
+# https://docs.gitlab.com/ee/development/gitaly.html#legacy-rugged-code
+# for more details.
+
+module Gitlab
+  module Git
+    module RuggedImpl
+      module Ref
+        def self.dereference_object(object)
+          object = object.target while object.is_a?(::Rugged::Tag::Annotation)
+
+          object
+        end
+      end
+    end
+  end
+end

lib/gitlab/git/rugged_impl/repository.rb

+# frozen_string_literal: true
+
+# NOTE: This code is legacy. Do not add/modify code here unless you have
+# discussed with the Gitaly team.  See
+# https://docs.gitlab.com/ee/development/gitaly.html#legacy-rugged-code
+# for more details.
+
+# rubocop:disable Gitlab/ModuleWithInstanceVariables
+module Gitlab
+  module Git
+    module RuggedImpl
+      module Repository
+        FEATURE_FLAGS = %i(rugged_find_commit).freeze
+
+        def alternate_object_directories
+          relative_object_directories.map { |d| File.join(path, d) }
+        end
+
+        ALLOWED_OBJECT_RELATIVE_DIRECTORIES_VARIABLES = %w[
+          GIT_OBJECT_DIRECTORY_RELATIVE
+          GIT_ALTERNATE_OBJECT_DIRECTORIES_RELATIVE
+        ].freeze
+
+        def relative_object_directories
+          Gitlab::Git::HookEnv.all(gl_repository).values_at(*ALLOWED_OBJECT_RELATIVE_DIRECTORIES_VARIABLES).flatten.compact
+        end
+
+        def rugged
+          @rugged ||= ::Rugged::Repository.new(path, alternates: alternate_object_directories)
+        rescue ::Rugged::RepositoryError, ::Rugged::OSError
+          raise ::Gitlab::Git::Repository::NoRepository.new('no repository for such path')
+        end
+
+        def cleanup
+          @rugged&.close
+        end
+
+        # Return the object that +revspec+ points to.  If +revspec+ is an
+        # annotated tag, then return the tag's target instead.
+        def rev_parse_target(revspec)
+          obj = rugged.rev_parse(revspec)
+          Ref.dereference_object(obj)
+        end
+      end
+    end
+  end
+end
+# rubocop:enable Gitlab/ModuleWithInstanceVariables

lib/gitlab/gitaly_client/storage_settings.rb

@@ -32,11 +32,19 @@ module Gitlab
       end
 
       def self.disk_access_denied?
+        return false if rugged_enabled?
+
         !temporarily_allowed?(ALLOW_KEY) && GitalyClient.feature_enabled?(DISK_ACCESS_DENIED_FLAG)
       rescue
         false # Err on the side of caution, don't break gitlab for people
       end
 
+      def self.rugged_enabled?
+        Gitlab::Git::RuggedImpl::Repository::FEATURE_FLAGS.any? do |flag|
+          Feature.enabled?(flag)
+        end
+      end
+
       def initialize(storage)
         raise InvalidConfigurationError, "expected a Hash, got a #{storage.class.name}" unless storage.is_a?(Hash)
         raise InvalidConfigurationError, INVALID_STORAGE_MESSAGE unless storage.has_key?('path')

lib/tasks/gitlab/features.rake

+namespace :gitlab do
+  namespace :features do
+    desc 'GitLab | Features | Enable direct Git access via Rugged for NFS'
+    task enable_rugged: :environment do
+      set_rugged_feature_flags(true)
+      puts 'All Rugged feature flags were enabled.'
+    end
+
+    task disable_rugged: :environment do
+      set_rugged_feature_flags(false)
+      puts 'All Rugged feature flags were disabled.'
+    end
+  end
+
+  def set_rugged_feature_flags(status)
+    Gitlab::Git::RuggedImpl::Repository::FEATURE_FLAGS.each do |flag|
+      if status
+        Feature.enable(flag)
+      else
+        Feature.disable(flag)
+      end
+    end
+  end
+end

scripts/lint-rugged

@@ -5,12 +5,18 @@ ALLOWED = [
   'lib/gitlab/bare_repository_import/repository.rb',
 
   # Needed to avoid using the git binary to validate a branch name
-  'lib/gitlab/git_ref_validator.rb'
+  'lib/gitlab/git_ref_validator.rb',
+
+  # Reverted Rugged calls due to Gitaly atop NFS performance
+  # See https://docs.gitlab.com/ee/development/gitaly.html#legacy-rugged-code.
+  'lib/gitlab/git/rugged_impl/',
+  'lib/gitlab/gitaly_client/storage_settings.rb'
 ].freeze
 
 rugged_lines = IO.popen(%w[git grep -i -n rugged -- app config lib], &:read).lines
 rugged_lines = rugged_lines.select { |l| /^[^:]*\.rb:/ =~ l }
 rugged_lines = rugged_lines.reject { |l| l.start_with?(*ALLOWED) }
+rugged_lines = rugged_lines.reject { |l| /(include|prepend) Gitlab::Git::RuggedImpl/ =~ l}
 rugged_lines = rugged_lines.reject do |line|
   code, _comment = line.split('# ', 2)
   code !~ /rugged/i

spec/lib/gitlab/git/commit_spec.rb

@@ -112,7 +112,7 @@ describe Gitlab::Git::Commit, :seed_helper do
   end
 
   context 'Class methods' do
-    describe '.find' do
+    shared_examples '.find' do
       it "should return first head commit if without params" do
         expect(described_class.last(repository).id).to eq(
           rugged_repo.head.target.oid
@@ -154,6 +154,20 @@ describe Gitlab::Git::Commit, :seed_helper do
       end
     end
 
+    describe '.find with Gitaly enabled' do
+      it_should_behave_like '.find'
+    end
+
+    describe '.find with Rugged enabled', :enable_rugged do
+      it 'calls out to the Rugged implementation' do
+        allow_any_instance_of(Rugged).to receive(:rev_parse).with(SeedRepo::Commit::ID).and_call_original
+
+        described_class.find(repository, SeedRepo::Commit::ID)
+      end
+
+      it_should_behave_like '.find'
+    end
+
     describe '.last_for_path' do
       context 'no path' do
         subject { described_class.last_for_path(repository, 'master') }

spec/lib/gitlab/gitaly_client/storage_settings_spec.rb

@@ -26,4 +26,14 @@ describe Gitlab::GitalyClient::StorageSettings do
       end
     end
   end
+
+  describe '.disk_access_denied?' do
+    it 'return false when Rugged is enabled', :enable_rugged do
+      expect(described_class.disk_access_denied?).to be_falsey
+    end
+
+    it 'returns true' do
+      expect(described_class.disk_access_denied?).to be_truthy
+    end
+  end
 end

spec/spec_helper.rb

@@ -115,10 +115,17 @@ RSpec.configure do |config|
     TestEnv.clean_test_path
   end
 
-  config.before do
+  config.before do |example|
     # Enable all features by default for testing
     allow(Feature).to receive(:enabled?) { true }
 
+    enabled = example.metadata[:enable_rugged].present?
+
+    # Disable Rugged features by default
+    Gitlab::Git::RuggedImpl::Repository::FEATURE_FLAGS.each do |flag|
+      allow(Feature).to receive(:enabled?).with(flag).and_return(enabled)
+    end
+
     # The following can be removed when we remove the staged rollout strategy
     # and we can just enable it using instance wide settings
     # (ie. ApplicationSetting#auto_devops_enabled)