Refresh project authorizations using a Redis leaserefresh-authorizations-with-lease

When I proposed using serializable transactions I was hoping we would be
able to refresh data of individual users concurrently. Unfortunately
upon closer inspection it was revealed this was not the case. This could
result in a lot of queries failing due to serialization errors,
overloading the database in the process (given enough workers trying to
update the target table).

To work around this we're now using a Redis lease that is cancelled upon
completion. This ensures we can update the data of different users
concurrently without overloading the database.

The code will try to obtain the lease until it succeeds, waiting at
least 1 second between retries. This is necessary as we may otherwise
end up _not_ updating the data which is not an option.

1 files changed, 21 insertions, 2 deletions

diff --git a/app/workers/authorized_projects_worker.rb b/app/workers/authorized_projects_worker.rb
index 331727ba9d8..fccddb70d18 100644
--- a/app/workers/authorized_projects_worker.rb
+++ b/app/workers/authorized_projects_worker.rb
@@ -2,14 +2,33 @@ class AuthorizedProjectsWorker
   include Sidekiq::Worker
   include DedicatedSidekiqQueue
 
+  LEASE_TIMEOUT = 1.minute.to_i
+
   def self.bulk_perform_async(args_list)
     Sidekiq::Client.push_bulk('class' => self, 'args' => args_list)
   end
 
   def perform(user_id)
     user = User.find_by(id: user_id)
-    return unless user
 
-    user.refresh_authorized_projects
+    refresh(user) if user
+  end
+
+  def refresh(user)
+    lease_key = "refresh_authorized_projects:#{user.id}"
+    lease = Gitlab::ExclusiveLease.new(lease_key, timeout: LEASE_TIMEOUT)
+
+    until uuid = lease.try_obtain
+      # Keep trying until we obtain the lease. If we don't do so we may end up
+      # not updating the list of authorized projects properly. To prevent
+      # hammering Redis too much we'll wait for a bit between retries.
+      sleep(1)
+    end
+
+    begin
+      user.refresh_authorized_projects
+    ensure
+      Gitlab::ExclusiveLease.cancel(lease_key, uuid)
+    end
   end
 end