Enable caching of schema.rbschema-cache

This is a lesser known Rails feature that removes the need for querying
various internal tables for schema details (e.g. column types) every
time Rails boots up.

This feature is described in http://iempire.ru/2016/12/13/schema-cache/
and was brought to our attention by @stanhu.

Since the schema cache is specific to the database we only enable this
on PostgreSQL.

6 files changed, 22 insertions, 4 deletions

diff --git a/.gitlab/merge_request_templates/Database Changes.md b/.gitlab/merge_request_templates/Database Changes.md
index 2a5c8267872..1e74f70d2ed 100644
--- a/.gitlab/merge_request_templates/Database Changes.md
+++ b/.gitlab/merge_request_templates/Database Changes.md
@@ -21,6 +21,7 @@ measurements there, and include the results in this MR.
 When adding migrations:
 
 - [ ] Updated `db/schema.rb`
+- [ ] Updated `db/schema_cache.dump`
 - [ ] Added a `down` method so the migration can be reverted
 - [ ] Added the output of the migration(s) to the MR body
 - [ ] Added the execution time of the migration(s) to the MR body
diff --git a/changelogs/unreleased/schema-cache.yml b/changelogs/unreleased/schema-cache.yml
new file mode 100644
index 00000000000..61f6e56f4cf
--- /dev/null
+++ b/changelogs/unreleased/schema-cache.yml
@@ -0,0 +1,5 @@
+---
+title: Enable caching of schema.rb
+merge_request:
+author:
+type: other
diff --git a/config/application.rb b/config/application.rb
index f69dab4de39..68dc449b793 100644
--- a/config/application.rb
+++ b/config/application.rb
@@ -10,6 +10,7 @@ module Gitlab
     require_dependency Rails.root.join('lib/gitlab/redis/queues')
     require_dependency Rails.root.join('lib/gitlab/redis/shared_state')
     require_dependency Rails.root.join('lib/gitlab/request_context')
+    require_dependency Rails.root.join('lib/gitlab/database')
 
     # Settings in config/environments/* take precedence over those specified here.
     # Application configuration should go into files in config/initializers
@@ -156,6 +157,10 @@ module Gitlab
 
     config.active_record.raise_in_transactional_callbacks = true
 
+    # The schema cache is database specific. There is no way to support both
+    # PostgreSQL and MySQL, hence we only enable this when PostgreSQL is used.
+    config.active_record.use_schema_cache_dump = Gitlab::Database.postgresql?
+
     config.active_job.queue_adapter = :sidekiq
 
     # This is needed for gitlab-shell
diff --git a/db/schema.rb b/db/schema.rb
index cd488630237..13c741bb8dd 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20170820100558) do
+ActiveRecord::Schema.define(version: 20170824162758) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -34,7 +34,7 @@ ActiveRecord::Schema.define(version: 20170820100558) do
     t.string "logo"
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
-    t.text "description_html", null: false
+    t.text "description_html"
     t.integer "cached_markdown_version"
   end
 
@@ -279,8 +279,8 @@ ActiveRecord::Schema.define(version: 20170820100558) do
     t.string "encrypted_value_salt"
     t.string "encrypted_value_iv"
     t.integer "pipeline_schedule_id", null: false
-    t.datetime "created_at"
-    t.datetime "updated_at"
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
   end
 
   add_index "ci_pipeline_schedule_variables", ["pipeline_schedule_id", "key"], name: "index_ci_pipeline_schedule_variables_on_schedule_id_and_key", unique: true, using: :btree
diff --git a/db/schema_cache.dump b/db/schema_cache.dump
new file mode 100644
index 00000000000..197014c1471
--- /dev/null
+++ b/db/schema_cache.dump
diff --git a/lib/tasks/db.rake b/lib/tasks/db.rake
new file mode 100644
index 00000000000..664e75494b8
--- /dev/null
+++ b/lib/tasks/db.rake
@@ -0,0 +1,7 @@
+namespace :db do
+  namespace :schema do
+    task 'dump' do
+      Rake::Task['db:schema:cache:dump'].invoke
+    end
+  end
+end