Allow external diffs to be used conditionally

Since external diffs are likely to be a bit slower than in-database
ones, add a mode that makes diffs external after they've been obsoleted
by events. This should strike a balance between performance and disk
space.

A background cron drives the majority of migrations, since diffs become
outdated through user actions.

1 files changed, 16 insertions, 0 deletions

diff --git a/spec/factories/merge_requests.rb b/spec/factories/merge_requests.rb
index a73f330a7a9..a1809a26265 100644
--- a/spec/factories/merge_requests.rb
+++ b/spec/factories/merge_requests.rb
@@ -46,10 +46,26 @@ FactoryBot.define do
       target_branch "improve/awesome"
     end
 
+    trait :merged_last_month do
+      merged
+
+      after(:build) do |merge_request|
+        merge_request.build_metrics.merged_at = 1.month.ago
+      end
+    end
+
     trait :closed do
       state :closed
     end
 
+    trait :closed_last_month do
+      closed
+
+      after(:build) do |merge_request|
+        merge_request.build_metrics.latest_closed_at = 1.month.ago
+      end
+    end
+
     trait :opened do
       state :opened
     end