Load and process at most 100 commits when pushing into default branch

app/services/git_push_service.rb

@@ -45,6 +45,7 @@ class GitPushService < BaseService
     elsif push_to_existing_branch?
       # Collect data for this git push
       @push_commits = @project.repository.commits_between(params[:oldrev], params[:newrev])
+
       process_commit_messages
 
       # Update the bare repositories info/attributes file using the contents of the default branches
@@ -64,15 +65,21 @@ class GitPushService < BaseService
 
   def update_caches
     if is_default_branch?
+      if push_to_new_branch?
+        # If this is the initial push into the default branch, the file type caches
+        # will already be reset as a result of `Project#change_head`.
+        types = []
+      else
         paths = Set.new
 
-      @push_commits.each do |commit|
+        @push_commits.last(PROCESS_COMMIT_LIMIT).each do |commit|
           commit.raw_deltas.each do |diff|
             paths << diff.new_path
           end
         end
 
         types = Gitlab::FileDetector.types_in_paths(paths.to_a)
+      end
     else
       types = []
     end
@@ -84,7 +91,7 @@ class GitPushService < BaseService
   def process_commit_messages
     default = is_default_branch?
 
-    push_commits.last(PROCESS_COMMIT_LIMIT).each do |commit|
+    @push_commits.last(PROCESS_COMMIT_LIMIT).each do |commit|
       if commit.matches_cross_reference_regex?
         ProcessCommitWorker
           .perform_async(project.id, current_user.id, commit.to_hash, default)
@@ -123,7 +130,10 @@ class GitPushService < BaseService
   end
 
   def process_default_branch
-    @push_commits = project.repository.commits(params[:newrev])
+    @push_commits_count = project.repository.commit_count_for_ref(params[:ref])
+
+    offset = [@push_commits_count - PROCESS_COMMIT_LIMIT, 0].max
+    @push_commits = project.repository.commits(params[:newrev], offset: offset, limit: PROCESS_COMMIT_LIMIT)
 
     # Ensure HEAD points to the default branch in case it is not master
     project.change_head(branch_name)
@@ -152,7 +162,8 @@ class GitPushService < BaseService
       params[:oldrev],
       params[:newrev],
       params[:ref],
-      push_commits)
+      @push_commits,
+      commits_count: @push_commits_count)
   end
 
   def push_to_existing_branch?

changelogs/unreleased/dm-large-push-performance.yml

+---
+title: Improve performance of large (initial) push into default branch
+merge_request:
+author:

lib/gitlab/data_builder/push.rb

@@ -24,11 +24,11 @@ module Gitlab
       #   total_commits_count: Fixnum
       # }
       #
-      def build(project, user, oldrev, newrev, ref, commits = [], message = nil)
+      def build(project, user, oldrev, newrev, ref, commits = [], message = nil, commits_count: nil)
         commits = Array(commits)
 
         # Total commits count
-        commits_count = commits.size
+        commits_count ||= commits.size
 
         # Get latest 20 commits ASC
         commits_limited = commits.last(20)

spec/services/git_push_service_spec.rb

@@ -663,8 +663,7 @@ describe GitPushService, services: true do
     end
 
     it 'only schedules a limited number of commits' do
-      allow(service).to receive(:push_commits)
-        .and_return(Array.new(1000, double(:commit, to_hash: {}, matches_cross_reference_regex?: true)))
+      service.push_commits = Array.new(1000, double(:commit, to_hash: {}, matches_cross_reference_regex?: true))
 
       expect(ProcessCommitWorker).to receive(:perform_async).exactly(100).times
 
@@ -672,8 +671,7 @@ describe GitPushService, services: true do
     end
 
     it "skips commits which don't include cross-references" do
-      allow(service).to receive(:push_commits)
-        .and_return([double(:commit, to_hash: {}, matches_cross_reference_regex?: false)])
+      service.push_commits = [double(:commit, to_hash: {}, matches_cross_reference_regex?: false)]
 
       expect(ProcessCommitWorker).not_to receive(:perform_async)