Instrument Rails cache code

This allows us to track how much time of a transaction is spent in
dealing with cached data.

1 files changed, 39 insertions, 0 deletions

diff --git a/lib/gitlab/metrics/subscribers/rails_cache.rb b/lib/gitlab/metrics/subscribers/rails_cache.rb
new file mode 100644
index 00000000000..49e5f86e6e6
--- /dev/null
+++ b/lib/gitlab/metrics/subscribers/rails_cache.rb
@@ -0,0 +1,39 @@
+module Gitlab
+  module Metrics
+    module Subscribers
+      # Class for tracking the total time spent in Rails cache calls
+      class RailsCache < ActiveSupport::Subscriber
+        attach_to :active_support
+
+        def cache_read(event)
+          increment(:cache_read_duration, event.duration)
+        end
+
+        def cache_write(event)
+          increment(:cache_write_duration, event.duration)
+        end
+
+        def cache_delete(event)
+          increment(:cache_delete_duration, event.duration)
+        end
+
+        def cache_exist?(event)
+          increment(:cache_exists_duration, event.duration)
+        end
+
+        def increment(key, duration)
+          return unless current_transaction
+
+          current_transaction.increment(:cache_duration, duration)
+          current_transaction.increment(key, duration)
+        end
+
+        private
+
+        def current_transaction
+          Transaction.current
+        end
+      end
+    end
+  end
+end