Merge branch 'fix_initial_push_mass_sql' into 'master'

Fix mass SQL statements during initial push of a big repository

## What does this MR do?
This MR prevents `process_commit_messages(ref)` to be executed for the initial push to the default branch.
Currently it is being executed which results in ~500000 SQL Statements during the import of the linux mainline repository.
These statements check for references to issues/mrs in each commit.
That usually doesn't make sense for the initial push, because there aren't any issues/mrs yet.

This MR will reduce the load on gitlab servers in the coming months. Especially now that several importers are available for gitlab and projects are moving from gitorious to gitlab.

See merge request !376

CHANGELOG

 Please view this file on the master branch, on stable branches it's out of date.
 
 v 7.9.0 (unreleased)
+  - Fix mass SQL statements on initial push (Hannes Rosenögger)
   - Add tag push notifications and normalize HipChat and Slack messages to be consistent (Stan Hu)
   - Add comment notification events to HipChat and Slack services (Stan Hu)
   - Add issue and merge request events to HipChat and Slack services (Stan Hu)

app/services/git_push_service.rb

@@ -42,8 +42,10 @@ class GitPushService
           # as a heuristic. This may include more commits than are actually pushed, but
           # that shouldn't matter because we check for existing cross-references later.
           @push_commits = project.repository.commits_between(project.default_branch, newrev)
-        end
+
+          # don't process commits for the initial push to the default branch
           process_commit_messages(ref)
+        end
       elsif push_to_existing_branch?(ref, oldrev)
         # Collect data for this git push
         @push_commits = project.repository.commits_between(oldrev, newrev)

spec/services/git_push_service_spec.rb

@@ -197,15 +197,6 @@ describe GitPushService do
 
       service.execute(project, user, @blankrev, @newrev, 'refs/heads/other')
     end
-
-    it "finds references in the first push to a default branch" do
-      allow(project.repository).to receive(:commits_between).with(@blankrev, @newrev).and_return([])
-      allow(project.repository).to receive(:commits).with(@newrev).and_return([commit])
-
-      expect(Note).to receive(:create_cross_reference_note).with(issue, commit, commit_author, project)
-
-      service.execute(project, user, @blankrev, @newrev, 'refs/heads/master')
-    end
   end
 
   describe "closing issues from pushed commits" do