Better caching and indexing of broadcast messages

Caching of BroadcastMessage instances has been changed so a cache stays
valid as long as the default cache expiration time permits, instead of
the cache being expired after 1 minute. When modifying broadcast
messages the cache is flushed automatically.

To remove the need for performing sequence scans on the
"broadcast_messages" table we also add an index on (starts_at, ends_at,
id), permitting PostgreSQL to use an index scan to get all necessary
data.

Finally this commit adds a few NOT NULL constraints to the table to
match the Rails validations.

Fixes gitlab-org/gitlab-ce#31706

1 files changed, 12 insertions, 2 deletions

diff --git a/app/models/broadcast_message.rb b/app/models/broadcast_message.rb
index 944725d91c3..3692bcc680d 100644
--- a/app/models/broadcast_message.rb
+++ b/app/models/broadcast_message.rb
@@ -14,9 +14,15 @@ class BroadcastMessage < ActiveRecord::Base
   default_value_for :color, '#E75E40'
   default_value_for :font,  '#FFFFFF'
 
+  CACHE_KEY = 'broadcast_message_current'.freeze
+
+  after_commit :flush_redis_cache
+
   def self.current
-    Rails.cache.fetch("broadcast_message_current", expires_in: 1.minute) do
-      where('ends_at > :now AND starts_at <= :now', now: Time.zone.now).order([:created_at, :id]).to_a
+    Rails.cache.fetch(CACHE_KEY) do
+      where('ends_at > :now AND starts_at <= :now', now: Time.zone.now)
+        .reorder(id: :asc)
+        .to_a
     end
   end
 
@@ -31,4 +37,8 @@ class BroadcastMessage < ActiveRecord::Base
   def ended?
     ends_at < Time.zone.now
   end
+
+  def flush_redis_cache
+    Rails.cache.delete(CACHE_KEY)
+  end
 end