Add race_condition_ttl support

Prevents multiple writes under heavy load.

lib/api/helpers/caching.rb

@@ -11,6 +11,11 @@ module API
       # @return [ActiveSupport::Duration]
       DEFAULT_EXPIRY = 1.day
 
+      # @return [Hash]
+      DEFAULT_CACHE_OPTIONS = {
+        race_condition_ttl: 5.seconds
+      }.freeze
+
       # @return [ActiveSupport::Cache::Store]
       def cache
         Rails.cache
@@ -75,7 +80,7 @@ module API
       # @param expires_in [ActiveSupport::Duration, Integer] an expiry time for the cache entry
       # @return [Gitlab::Json::PrecompiledJson]
       def cache_action(key, **cache_opts)
-        json = cache.fetch(key, **cache_opts) do
+        json = cache.fetch(key, **apply_default_cache_options(cache_opts)) do
           Gitlab::Json.dump(yield.as_json)
         end
 
@@ -106,6 +111,10 @@ module API
 
       private
 
+      def apply_default_cache_options(opts = {})
+        DEFAULT_CACHE_OPTIONS.merge(opts)
+      end
+
       # Optionally uses a `Proc` to add context to a cache key
       #
       # @param object [Object] must respond to #cache_key

spec/lib/api/helpers/caching_spec.rb

@@ -170,8 +170,10 @@ RSpec.describe API::Helpers::Caching, :use_clean_rails_redis_caching do
     end
 
     it "only calls the expensive action once" do
+      expected_kwargs = described_class::DEFAULT_CACHE_OPTIONS.merge(kwargs)
+
       expect(expensive_thing).to receive(:do_very_expensive_action).once
-      expect(instance.cache).to receive(:fetch).with(cache_key, **kwargs).exactly(5).times.and_call_original
+      expect(instance.cache).to receive(:fetch).with(cache_key, **expected_kwargs).exactly(5).times.and_call_original
 
       5.times { perform }
     end