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, 19 insertions, 1 deletions

diff --git a/spec/models/broadcast_message_spec.rb b/spec/models/broadcast_message_spec.rb
index a8ca1d110e4..3369aef1d3e 100644
--- a/spec/models/broadcast_message_spec.rb
+++ b/spec/models/broadcast_message_spec.rb
@@ -20,7 +20,7 @@ describe BroadcastMessage do
     it { is_expected.not_to allow_value('000').for(:font) }
   end
 
-  describe '.current' do
+  describe '.current', :use_clean_rails_memory_store_caching do
     it 'returns message if time match' do
       message = create(:broadcast_message)
 
@@ -45,6 +45,14 @@ describe BroadcastMessage do
 
       expect(described_class.current).to be_empty
     end
+
+    it 'caches the output of the query' do
+      create(:broadcast_message)
+
+      expect(described_class).to receive(:where).and_call_original.once
+
+      2.times { described_class.current }
+    end
   end
 
   describe '#active?' do
@@ -102,4 +110,14 @@ describe BroadcastMessage do
       end
     end
   end
+
+  describe '#flush_redis_cache' do
+    it 'flushes the Redis cache' do
+      message = create(:broadcast_message)
+
+      expect(Rails.cache).to receive(:delete).with(described_class::CACHE_KEY)
+
+      message.flush_redis_cache
+    end
+  end
 end