Move pushes_since_gc to Redis

This moves tracking of the pushes since the last Git GC from PostgreSQL
to Redis. This reduces the number of writes on the "projects" table.
This in turn reduces the vacuuming overhead.

The lease used for incrementing the counter has been removed. This lease
was mostly put in place to prevent high database load but this isn't
needed anymore due to the counter now being stored in Redis.

Fixes gitlab-org/gitlab-ce#22125

2 files changed, 19 insertions, 9 deletions

diff --git a/app/models/project.rb b/app/models/project.rb
index 4017cabe9f0..f3f3ffbbd28 100644
--- a/app/models/project.rb
+++ b/app/models/project.rb
@@ -1288,8 +1288,24 @@ class Project < ActiveRecord::Base
     end
   end
 
+  def pushes_since_gc
+    Gitlab::Redis.with { |redis| redis.get(pushes_since_gc_redis_key).to_i }
+  end
+
+  def increment_pushes_since_gc
+    Gitlab::Redis.with { |redis| redis.incr(pushes_since_gc_redis_key) }
+  end
+
+  def reset_pushes_since_gc
+    Gitlab::Redis.with { |redis| redis.del(pushes_since_gc_redis_key) }
+  end
+
   private
 
+  def pushes_since_gc_redis_key
+    "projects/#{id}/pushes_since_gc"
+  end
+
   # Prevents the creation of project_feature record for every project
   def setup_project_feature
     build_project_feature unless project_feature
diff --git a/app/services/projects/housekeeping_service.rb b/app/services/projects/housekeeping_service.rb
index 29b3981f49f..c3dfc8cfbe8 100644
--- a/app/services/projects/housekeeping_service.rb
+++ b/app/services/projects/housekeeping_service.rb
@@ -30,10 +30,8 @@ module Projects
     end
 
     def increment!
-      if Gitlab::ExclusiveLease.new("project_housekeeping:increment!:#{@project.id}", timeout: 60).try_obtain
-        Gitlab::Metrics.measure(:increment_pushes_since_gc) do
-          update_pushes_since_gc(@project.pushes_since_gc + 1)
-        end
+      Gitlab::Metrics.measure(:increment_pushes_since_gc) do
+        @project.increment_pushes_since_gc
       end
     end
 
@@ -43,14 +41,10 @@ module Projects
       GitGarbageCollectWorker.perform_async(@project.id)
     ensure
       Gitlab::Metrics.measure(:reset_pushes_since_gc) do
-        update_pushes_since_gc(0)
+        @project.reset_pushes_since_gc
       end
     end
 
-    def update_pushes_since_gc(new_value)
-      @project.update_column(:pushes_since_gc, new_value)
-    end
-
     def try_obtain_lease
       Gitlab::Metrics.measure(:obtain_housekeeping_lease) do
         lease = ::Gitlab::ExclusiveLease.new("project_housekeeping:#{@project.id}", timeout: LEASE_TIMEOUT)