Refine Git garbage collection

app/controllers/admin/application_settings_controller.rb

@@ -117,6 +117,11 @@ class Admin::ApplicationSettingsController < Admin::ApplicationController
       :send_user_confirmation_email,
       :container_registry_token_expire_delay,
       :enabled_git_access_protocol,
+      :housekeeping_enabled,
+      :housekeeping_bitmaps_enabled,
+      :housekeeping_incremental_repack_period,
+      :housekeeping_full_repack_period,
+      :housekeeping_gc_period,
       repository_storages: [],
       restricted_visibility_levels: [],
       import_sources: [],

app/models/application_setting.rb

@@ -85,6 +85,18 @@ class ApplicationSetting < ActiveRecord::Base
             presence: { message: 'Domain blacklist cannot be empty if Blacklist is enabled.' },
             if: :domain_blacklist_enabled?
 
+  validates :housekeeping_incremental_repack_period,
+            presence: true,
+            numericality: { only_integer: true, greater_than: 0 }
+
+  validates :housekeeping_full_repack_period,
+            presence: true,
+            numericality: { only_integer: true, greater_than: :housekeeping_incremental_repack_period }
+
+  validates :housekeeping_gc_period,
+            presence: true,
+            numericality: { only_integer: true, greater_than: :housekeeping_full_repack_period }
+
   validates_each :restricted_visibility_levels do |record, attr, value|
     unless value.nil?
       value.each do |level|
@@ -168,6 +180,11 @@ class ApplicationSetting < ActiveRecord::Base
       container_registry_token_expire_delay: 5,
       repository_storages: ['default'],
       user_default_external: false,
+      housekeeping_enabled: true,
+      housekeeping_bitmaps_enabled: true,
+      housekeeping_incremental_repack_period: 10,
+      housekeeping_full_repack_period: 50,
+      housekeeping_gc_period: 200,
     )
   end
 

app/services/projects/housekeeping_service.rb

@@ -7,6 +7,8 @@
 #
 module Projects
   class HousekeepingService < BaseService
+    include Gitlab::CurrentSettings
+
     LEASE_TIMEOUT = 3600
 
     class LeaseTaken < StandardError
@@ -20,13 +22,14 @@ module Projects
     end
 
     def execute
-      raise LeaseTaken unless try_obtain_lease
+      lease_uuid = try_obtain_lease
+      raise LeaseTaken unless lease_uuid.present?
 
-      execute_gitlab_shell_gc
+      execute_gitlab_shell_gc(lease_uuid)
     end
 
     def needed?
-      @project.pushes_since_gc >= 10
+      pushes_since_gc > 0 && period_match? && housekeeping_enabled?
     end
 
     def increment!
@@ -37,19 +40,59 @@ module Projects
 
     private
 
-    def execute_gitlab_shell_gc
-      GitGarbageCollectWorker.perform_async(@project.id)
+    def execute_gitlab_shell_gc(lease_uuid)
+      GitGarbageCollectWorker.perform_async(@project.id, task, lease_key, lease_uuid)
     ensure
-      Gitlab::Metrics.measure(:reset_pushes_since_gc) do
-        @project.reset_pushes_since_gc
+      if pushes_since_gc >= gc_period
+        Gitlab::Metrics.measure(:reset_pushes_since_gc) do
+          @project.reset_pushes_since_gc
+        end
       end
     end
 
     def try_obtain_lease
       Gitlab::Metrics.measure(:obtain_housekeeping_lease) do
-        lease = ::Gitlab::ExclusiveLease.new("project_housekeeping:#{@project.id}", timeout: LEASE_TIMEOUT)
+        lease = ::Gitlab::ExclusiveLease.new(lease_key, timeout: LEASE_TIMEOUT)
         lease.try_obtain
       end
     end
+
+    def lease_key
+      "project_housekeeping:#{@project.id}"
+    end
+
+    def pushes_since_gc
+      @project.pushes_since_gc
+    end
+
+    def task
+      if pushes_since_gc % gc_period == 0
+        :gc
+      elsif pushes_since_gc % full_repack_period == 0
+        :full_repack
+      else
+        :incremental_repack
+      end
+    end
+
+    def period_match?
+      [gc_period, full_repack_period, repack_period].any? { |period| pushes_since_gc % period == 0 }
+    end
+
+    def housekeeping_enabled?
+      current_application_settings.housekeeping_enabled
+    end
+
+    def gc_period
+      current_application_settings.housekeeping_gc_period
+    end
+
+    def full_repack_period
+      current_application_settings.housekeeping_full_repack_period
+    end
+
+    def repack_period
+      current_application_settings.housekeeping_incremental_repack_period
+    end
   end
 end

app/views/admin/application_settings/_form.html.haml

@@ -422,5 +422,44 @@
             Enable this option to include the name of the author of the issue,
             merge request or comment in the email body instead.
 
+  %fieldset
+    %legend Automatic Git repository housekeeping
+    .form-group
+      .col-sm-offset-2.col-sm-10
+        .checkbox
+          = f.label :housekeeping_enabled do
+            = f.check_box :housekeeping_enabled
+            Enable automatic repository housekeeping (git repack, git gc)
+          .help-block
+            If you keep automatic housekeeping disabled for a long time Git
+            repository access on your GitLab server will become slower and your
+            repositories will use more disk space. We recommend to always leave
+            this enabled.
+        .checkbox
+          = f.label :housekeeping_bitmaps_enabled do
+            = f.check_box :housekeeping_bitmaps_enabled
+            Enable Git pack file bitmap creation
+          .help-block
+            Creating pack file bitmaps makes housekeeping take a little longer but
+            bitmaps should accelerate 'git clone' performance.
+    .form-group
+      = f.label :housekeeping_incremental_repack_period, 'Incremental repack period', class: 'control-label col-sm-2'
+      .col-sm-10
+        = f.number_field :housekeeping_incremental_repack_period, class: 'form-control'
+        .help-block
+          Number of Git pushes after which an incremental 'git repack' is run.
+    .form-group
+      = f.label :housekeeping_full_repack_period, 'Full repack period', class: 'control-label col-sm-2'
+      .col-sm-10
+        = f.number_field :housekeeping_full_repack_period, class: 'form-control'
+        .help-block
+          Number of Git pushes after which a full 'git repack' is run.
+    .form-group
+      = f.label :housekeeping_gc_period, 'Git GC period', class: 'control-label col-sm-2'
+      .col-sm-10
+        = f.number_field :housekeeping_gc_period, class: 'form-control'
+        .help-block
+          Number of Git pushes after which 'git gc' is run.
+
   .form-actions
     = f.submit 'Save', class: 'btn btn-save'

app/workers/git_garbage_collect_worker.rb

 class GitGarbageCollectWorker
   include Sidekiq::Worker
-  include Gitlab::ShellAdapter
   include DedicatedSidekiqQueue
+  include Gitlab::CurrentSettings
 
   sidekiq_options retry: false
 
-  def perform(project_id)
+  def perform(project_id, task = :gc, lease_key = nil, lease_uuid = nil)
     project = Project.find(project_id)
+    task = task.to_sym
+
+    cmd = command(task)
+    repo_path = project.repository.path_to_repo
+    description = "'#{cmd.join(' ')}' in #{repo_path}"
+
+    Gitlab::GitLogger.info(description)
+
+    output, status = Gitlab::Popen.popen(cmd, repo_path)
+    Gitlab::GitLogger.error("#{description} failed:\n#{output}") unless status.zero?
 
-    gitlab_shell.gc(project.repository_storage_path, project.path_with_namespace)
     # Refresh the branch cache in case garbage collection caused a ref lookup to fail
+    flush_ref_caches(project) if task == :gc
+  ensure
+    Gitlab::ExclusiveLease.cancel(lease_key, lease_uuid) if lease_key.present? && lease_uuid.present?
+  end
+
+  private
+
+  def command(task)
+    case task
+    when :gc
+      git(write_bitmaps: bitmaps_enabled?) + %w[gc]
+    when :full_repack
+      git(write_bitmaps: bitmaps_enabled?) + %w[repack -A -d --pack-kept-objects]
+    when :incremental_repack
+      # Normal git repack fails when bitmaps are enabled. It is impossible to
+      # create a bitmap here anyway.
+      git(write_bitmaps: false) + %w[repack -d]
+    else
+      raise "Invalid gc task: #{task.inspect}"
+    end
+  end
+
+  def flush_ref_caches(project)
     project.repository.after_create_branch
     project.repository.branch_names
     project.repository.has_visible_content?
   end
+
+  def bitmaps_enabled?
+    current_application_settings.housekeeping_bitmaps_enabled
+  end
+
+  def git(write_bitmaps:)
+    config_value = write_bitmaps ? 'true' : 'false'
+    %W[git -c repack.writeBitmaps=#{config_value}]
+  end
 end

changelogs/unreleased/git-gc-improvements.yml

+---
+title: Finer-grained Git gargage collection
+merge_request: 6588
+author: 

db/migrate/20161031155516_add_housekeeping_to_application_settings.rb

+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class AddHousekeepingToApplicationSettings < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  # Set this constant to true if this migration requires downtime.
+  DOWNTIME = false
+
+  # When a migration requires downtime you **must** uncomment the following
+  # constant and define a short and easy to understand explanation as to why the
+  # migration requires downtime.
+  # DOWNTIME_REASON = ''
+
+  disable_ddl_transaction!
+
+  def up
+    add_column_with_default(:application_settings, :housekeeping_enabled, :boolean, default: true, allow_null: false)
+    add_column_with_default(:application_settings, :housekeeping_bitmaps_enabled, :boolean, default: true, allow_null: false)
+    add_column_with_default(:application_settings, :housekeeping_incremental_repack_period, :integer, default: 10, allow_null: false)
+    add_column_with_default(:application_settings, :housekeeping_full_repack_period, :integer, default: 50, allow_null: false)
+    add_column_with_default(:application_settings, :housekeeping_gc_period, :integer, default: 200, allow_null: false)
+  end
+
+  def down
+    remove_column(:application_settings, :housekeeping_enabled, :boolean, default: true, allow_null: false)
+    remove_column(:application_settings, :housekeeping_bitmaps_enabled, :boolean, default: true, allow_null: false)
+    remove_column(:application_settings, :housekeeping_incremental_repack_period, :integer, default: 10, allow_null: false)
+    remove_column(:application_settings, :housekeeping_full_repack_period, :integer, default: 50, allow_null: false)
+    remove_column(:application_settings, :housekeeping_gc_period, :integer, default: 200, allow_null: false)
+  end
+end

db/schema.rb

@@ -98,6 +98,11 @@ ActiveRecord::Schema.define(version: 20161103171205) do
     t.text "help_page_text_html"
     t.text "shared_runners_text_html"
     t.text "after_sign_up_text_html"
+    t.boolean "housekeeping_enabled", default: true, null: false
+    t.boolean "housekeeping_bitmaps_enabled", default: true, null: false
+    t.integer "housekeeping_incremental_repack_period", default: 10, null: false
+    t.integer "housekeeping_full_repack_period", default: 50, null: false
+    t.integer "housekeeping_gc_period", default: 200, null: false
   end
 
   create_table "audit_events", force: :cascade do |t|

doc/administration/housekeeping.md

@@ -3,6 +3,14 @@
 > [Introduced][ce-2371] in GitLab 8.4.
 
 ---
+## Automatic housekeeping
+
+GitLab automatically runs `git gc` and `git repack` on repositories
+after Git pushes. If needed you can change how often this happens, or
+to turn it off, go to **Admin area > Settings**
+(`/admin/application_settings`).
+
+## Manual housekeeping
 
 The housekeeping function runs `git gc` ([man page][man]) on the current
 project Git repository.

lib/gitlab/backend/shell.rb

@@ -127,19 +127,6 @@ module Gitlab
                                    'rm-project', storage, "#{name}.git"])
     end
 
-    # Gc repository
-    #
-    # storage - project storage path
-    # path - project path with namespace
-    #
-    # Ex.
-    #   gc("/path/to/storage", "gitlab/gitlab-ci")
-    #
-    def gc(storage, path)
-      Gitlab::Utils.system_silent([gitlab_shell_projects_path, 'gc',
-                                   storage, "#{path}.git"])
-    end
-
     # Add new key to gitlab-shell
     #
     # Ex.

lib/gitlab/exclusive_lease.rb

+require 'securerandom'
+
 module Gitlab
   # This class implements an 'exclusive lease'. We call it a 'lease'
   # because it has a set expiry time. We call it 'exclusive' because only
   # one caller may obtain a lease for a given key at a time. The
   # implementation is intended to work across GitLab processes and across
-  # servers. It is a 'cheap' alternative to using SQL queries and updates:
+  # servers. It is a cheap alternative to using SQL queries and updates:
   # you do not need to change the SQL schema to start using
   # ExclusiveLease.
   #
-  # It is important to choose the timeout wisely. If the timeout is very
-  # high (1 hour) then the throughput of your operation gets very low (at
-  # most once an hour). If the timeout is lower than how long your
-  # operation may take then you cannot count on exclusivity. For example,
-  # if the timeout is 10 seconds and you do an operation which may take 20
-  # seconds then two overlapping operations may hold a lease for the same
-  # key at the same time.
-  #
-  # This class has no 'cancel' method. I originally decided against adding
-  # it because it would add complexity and a false sense of security. The
-  # complexity: instead of setting '1' we would have to set a UUID, and to
-  # delete it we would have to execute Lua on the Redis server to only
-  # delete the key if the value was our own UUID. Otherwise there is a
-  # chance that when you intend to cancel your lease you actually delete
-  # someone else's. The false sense of security: you cannot design your
-  # system to rely too much on the lease being cancelled after use because
-  # the calling (Ruby) process may crash or be killed. You _cannot_ count
-  # on begin/ensure blocks to cancel a lease, because the 'ensure' does
-  # not always run. Think of 'kill -9' from the Unicorn master for
-  # instance.
-  #
-  # If you find that leases are getting in your way, ask yourself: would
-  # it be enough to lower the lease timeout? Another thing that might be
-  # appropriate is to only use a lease for bulk/automated operations, and
-  # to ignore the lease when you get a single 'manual' user request (a
-  # button click).
-  #
   class ExclusiveLease
+    LUA_CANCEL_SCRIPT = <<-EOS
+      local key, uuid = KEYS[1], ARGV[1]
+      if redis.call("get", key) == uuid then
+        redis.call("del", key)
+      end
+    EOS
+
+    def self.cancel(key, uuid)
+      Gitlab::Redis.with do |redis|
+        redis.eval(LUA_CANCEL_SCRIPT, keys: [redis_key(key)], argv: [uuid])
+      end
+    end
+
+    def self.redis_key(key)
+      "gitlab:exclusive_lease:#{key}"
+    end
+
     def initialize(key, timeout:)
-      @key, @timeout = key, timeout
+      @redis_key = self.class.redis_key(key)
+      @timeout = timeout
+      @uuid = SecureRandom.uuid
     end
 
-    # Try to obtain the lease. Return true on success,
+    # Try to obtain the lease. Return lease UUID on success,
     # false if the lease is already taken.
     def try_obtain
       # Performing a single SET is atomic
       Gitlab::Redis.with do |redis|
-        !!redis.set(redis_key, '1', nx: true, ex: @timeout)
+        redis.set(@redis_key, @uuid, nx: true, ex: @timeout) && @uuid
       end
     end
 
     # Returns true if the key for this lease is set.
     def exists?
       Gitlab::Redis.with do |redis|
-        redis.exists(redis_key)
+        redis.exists(@redis_key)
       end
     end
-
-    # No #cancel method. See comments above!
-
-    private
-
-    def redis_key
-      "gitlab:exclusive_lease:#{@key}"
-    end
   end
 end

spec/lib/gitlab/backend/shell_spec.rb

@@ -14,7 +14,6 @@ describe Gitlab::Shell, lib: true do
   it { is_expected.to respond_to :add_repository }
   it { is_expected.to respond_to :remove_repository }
   it { is_expected.to respond_to :fork_repository }
-  it { is_expected.to respond_to :gc }
   it { is_expected.to respond_to :add_namespace }
   it { is_expected.to respond_to :rm_namespace }
   it { is_expected.to respond_to :mv_namespace }

spec/lib/gitlab/exclusive_lease_spec.rb

@@ -5,32 +5,47 @@ describe Gitlab::ExclusiveLease, type: :redis do
 
   describe '#try_obtain' do
     it 'cannot obtain twice before the lease has expired' do
-      lease = Gitlab::ExclusiveLease.new(unique_key, timeout: 3600)
-      expect(lease.try_obtain).to eq(true)
+      lease = described_class.new(unique_key, timeout: 3600)
+      expect(lease.try_obtain).to be_present
       expect(lease.try_obtain).to eq(false)
     end
 
     it 'can obtain after the lease has expired' do
       timeout = 1
-      lease = Gitlab::ExclusiveLease.new(unique_key, timeout: timeout)
+      lease = described_class.new(unique_key, timeout: timeout)
       lease.try_obtain # start the lease
       sleep(2 * timeout) # lease should have expired now
-      expect(lease.try_obtain).to eq(true)
+      expect(lease.try_obtain).to be_present
     end
   end
 
   describe '#exists?' do
     it 'returns true for an existing lease' do
-      lease = Gitlab::ExclusiveLease.new(unique_key, timeout: 3600)
+      lease = described_class.new(unique_key, timeout: 3600)
       lease.try_obtain
 
       expect(lease.exists?).to eq(true)
     end
 
     it 'returns false for a lease that does not exist' do
-      lease = Gitlab::ExclusiveLease.new(unique_key, timeout: 3600)
+      lease = described_class.new(unique_key, timeout: 3600)
 
       expect(lease.exists?).to eq(false)
     end
   end
+
+  describe '.cancel' do
+    it 'can cancel a lease' do
+      uuid = new_lease(unique_key)
+      expect(uuid).to be_present
+      expect(new_lease(unique_key)).to eq(false)
+
+      described_class.cancel(unique_key, uuid)
+      expect(new_lease(unique_key)).to be_present
+    end
+
+    def new_lease(key)
+      described_class.new(key, timeout: 3600).try_obtain
+    end
+  end
 end

spec/models/application_setting_spec.rb

@@ -98,6 +98,24 @@ describe ApplicationSetting, models: true do
         end
       end
     end
+
+    context 'housekeeping settings' do
+      it { is_expected.not_to allow_value(0).for(:housekeeping_incremental_repack_period) }
+
+      it 'wants the full repack period to be longer than the incremental repack period' do
+        subject.housekeeping_incremental_repack_period = 2
+        subject.housekeeping_full_repack_period = 1
+
+        expect(subject).not_to be_valid
+      end
+
+      it 'wants the gc period to be longer than the full repack period' do
+        subject.housekeeping_full_repack_period = 2
+        subject.housekeeping_gc_period = 1
+
+        expect(subject).not_to be_valid
+      end
+    end
   end
 
   context 'restricted signup domains' do

spec/services/projects/housekeeping_service_spec.rb

@@ -14,8 +14,10 @@ describe Projects::HousekeepingService do
 
   describe '#execute' do
     it 'enqueues a sidekiq job' do
-      expect(subject).to receive(:try_obtain_lease).and_return(true)
-      expect(GitGarbageCollectWorker).to receive(:perform_async).with(project.id)
+      expect(subject).to receive(:try_obtain_lease).and_return(:the_uuid)
+      expect(subject).to receive(:lease_key).and_return(:the_lease_key)
+      expect(subject).to receive(:task).and_return(:the_task)
+      expect(GitGarbageCollectWorker).to receive(:perform_async).with(project.id, :the_task, :the_lease_key, :the_uuid)
 
       subject.execute
       expect(project.reload.pushes_since_gc).to eq(0)
@@ -58,4 +60,26 @@ describe Projects::HousekeepingService do
       end.to change { project.pushes_since_gc }.from(0).to(1)
     end
   end
+
+  it 'uses all three kinds of housekeeping we offer' do
+    allow(subject).to receive(:try_obtain_lease).and_return(:the_uuid)
+    allow(subject).to receive(:lease_key).and_return(:the_lease_key)
+
+    # At push 200
+    expect(GitGarbageCollectWorker).to receive(:perform_async).with(project.id, :gc, :the_lease_key, :the_uuid).
+      exactly(1).times
+    # At push 50, 100, 150
+    expect(GitGarbageCollectWorker).to receive(:perform_async).with(project.id, :full_repack, :the_lease_key, :the_uuid).
+      exactly(3).times
+    # At push 10, 20, ... (except those above)
+    expect(GitGarbageCollectWorker).to receive(:perform_async).with(project.id, :incremental_repack, :the_lease_key, :the_uuid).
+      exactly(16).times
+
+    201.times do
+      subject.increment!
+      subject.execute if subject.needed?
+    end
+
+    expect(project.pushes_since_gc).to eq(1)
+  end
 end

spec/workers/git_garbage_collect_worker_spec.rb

+require 'digest'
+require 'fileutils'
+
 require 'spec_helper'
 
 describe GitGarbageCollectWorker do
@@ -6,16 +9,12 @@ describe GitGarbageCollectWorker do
 
   subject { GitGarbageCollectWorker.new }
 
-  before do
-    allow(subject).to receive(:gitlab_shell).and_return(shell)
-  end
-
   describe "#perform" do
-    it "runs `git gc`" do
-      expect(shell).to receive(:gc).with(
-        project.repository_storage_path,
-        project.path_with_namespace).
-      and_return(true)
+    it "flushes ref caches when the task is 'gc'" do
+      expect(subject).to receive(:command).with(:gc).and_return([:the, :command])
+      expect(Gitlab::Popen).to receive(:popen).
+        with([:the, :command], project.repository.path_to_repo).and_return(["", 0])
+
       expect_any_instance_of(Repository).to receive(:after_create_branch).and_call_original
       expect_any_instance_of(Repository).to receive(:branch_names).and_call_original
       expect_any_instance_of(Repository).to receive(:branch_count).and_call_original
@@ -23,5 +22,110 @@ describe GitGarbageCollectWorker do
 
       subject.perform(project.id)
     end
+
+    shared_examples 'gc tasks' do
+      before { allow(subject).to receive(:bitmaps_enabled?).and_return(bitmaps_enabled) }
+
+      it 'incremental repack adds a new packfile' do
+        create_objects(project)
+        before_packs = packs(project)
+
+        expect(before_packs.count).to be >= 1
+
+        subject.perform(project.id, 'incremental_repack')
+        after_packs = packs(project)
+
+        # Exactly one new pack should have been created
+        expect(after_packs.count).to eq(before_packs.count + 1)
+
+        # Previously existing packs are still around
+        expect(before_packs & after_packs).to eq(before_packs)
+      end
+
+      it 'full repack consolidates into 1 packfile' do
+        create_objects(project)
+        subject.perform(project.id, 'incremental_repack')
+        before_packs = packs(project)
+
+        expect(before_packs.count).to be >= 2
+
+        subject.perform(project.id, 'full_repack')
+        after_packs = packs(project)
+
+        expect(after_packs.count).to eq(1)
+
+        # Previously existing packs should be gone now
+        expect(after_packs - before_packs).to eq(after_packs)
+
+        expect(File.exist?(bitmap_path(after_packs.first))).to eq(bitmaps_enabled)
+      end
+
+      it 'gc consolidates into 1 packfile and updates packed-refs' do
+        create_objects(project)
+        before_packs = packs(project)
+        before_packed_refs = packed_refs(project)
+
+        expect(before_packs.count).to be >= 1
+
+        subject.perform(project.id, 'gc')
+        after_packed_refs = packed_refs(project)
+        after_packs = packs(project)
+
+        expect(after_packs.count).to eq(1)
+
+        # Previously existing packs should be gone now
+        expect(after_packs - before_packs).to eq(after_packs)
+
+        # The packed-refs file should have been updated during 'git gc'
+        expect(before_packed_refs).not_to eq(after_packed_refs)
+
+        expect(File.exist?(bitmap_path(after_packs.first))).to eq(bitmaps_enabled)
+      end
+    end
+
+    context 'with bitmaps enabled' do
+      let(:bitmaps_enabled) { true }
+
+      include_examples 'gc tasks'
+    end
+
+    context 'with bitmaps disabled' do
+      let(:bitmaps_enabled) { false }
+
+      include_examples 'gc tasks'
+    end
+  end
+
+  # Create a new commit on a random new branch
+  def create_objects(project)
+    rugged = project.repository.rugged
+    old_commit = rugged.branches.first.target
+    new_commit_sha = Rugged::Commit.create(
+      rugged,
+      message: "hello world #{SecureRandom.hex(6)}",
+      author: Gitlab::Git::committer_hash(email: 'foo@bar', name: 'baz'),
+      committer: Gitlab::Git::committer_hash(email: 'foo@bar', name: 'baz'),
+      tree: old_commit.tree,
+      parents: [old_commit],
+    )
+    project.repository.update_ref!(
+      "refs/heads/#{SecureRandom.hex(6)}",
+      new_commit_sha,
+      Gitlab::Git::BLANK_SHA
+    )
+  end
+
+  def packs(project)
+    Dir["#{project.repository.path_to_repo}/objects/pack/*.pack"]
+  end
+
+  def packed_refs(project)
+    path = "#{project.repository.path_to_repo}/packed-refs"
+    FileUtils.touch(path)
+    File.read(path)
+  end
+
+  def bitmap_path(pack)
+    pack.sub(/\.pack\z/, '.bitmap')
   end
 end