Memoize `get_all_versions` to reduce number of DB queries in testssh-speed-up-get-all-versions-test

Every time we access `ApplicationSetting` (e.g. when creating a user), we
also run `ActiveRecord::Migrator.needs_migration`:

```ruby
def needs_migration?(connection = Base.connection)
  (migrations(migrations_paths).collect(&:version) - get_all_versions(connection)).size > 0
end
```

During tests, we memoized the `migrations` call, saving a lot of filesystem
loads. However, we left `get_all_versions` alone. This patch memoizes that
as well to reduce DB and memory loads for that table.

See https://gitlab.com/gitlab-org/gitlab-ce/issues/24899#note_21207429

1 files changed, 5 insertions, 0 deletions

diff --git a/config/initializers/ar_speed_up_migration_checking.rb b/config/initializers/ar_speed_up_migration_checking.rb
index 1fe5defc01d..d61e2230b54 100644
--- a/config/initializers/ar_speed_up_migration_checking.rb
+++ b/config/initializers/ar_speed_up_migration_checking.rb
@@ -5,6 +5,7 @@ if Rails.env.test?
     class Migrator
       class << self
         alias_method :migrations_unmemoized, :migrations
+        alias_method :get_all_versions_unmemoized, :get_all_versions
 
         # This method is called a large number of times per rspec example, and
         # it reads + parses `db/migrate/*` each time. Memoizing it can save 0.5
@@ -12,6 +13,10 @@ if Rails.env.test?
         def migrations(paths)
           @migrations ||= migrations_unmemoized(paths)
         end
+
+        def get_all_versions(connection = Base.connection)
+          @all_versions ||= get_all_versions_unmemoized(connection)
+        end
       end
     end
   end