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, 7 insertions, 5 deletions

diff --git a/db/schema.rb b/db/schema.rb
index 65afe37a21c..9d3b3ad1826 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -163,16 +163,18 @@ ActiveRecord::Schema.define(version: 20170809142252) do
 
   create_table "broadcast_messages", force: :cascade do |t|
     t.text "message", null: false
-    t.datetime "starts_at"
-    t.datetime "ends_at"
-    t.datetime "created_at"
-    t.datetime "updated_at"
+    t.datetime "starts_at", null: false
+    t.datetime "ends_at", null: false
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
     t.string "color"
     t.string "font"
-    t.text "message_html"
+    t.text "message_html", null: false
     t.integer "cached_markdown_version"
   end
 
+  add_index "broadcast_messages", ["starts_at", "ends_at", "id"], name: "index_broadcast_messages_on_starts_at_and_ends_at_and_id", using: :btree
+
   create_table "chat_names", force: :cascade do |t|
     t.integer "user_id", null: false
     t.integer "service_id", null: false