Support Optimizer Hints

We as Arm Treasure Data are using Optimizer Hints with a monkey patch
(https://gist.github.com/kamipo/4c8539f0ce4acf85075cf5a6b0d9712e),
especially in order to use `MAX_EXECUTION_TIME` (refer #31129).

Example:

```ruby
class Job < ApplicationRecord
  default_scope { optimizer_hints("MAX_EXECUTION_TIME(50000) NO_INDEX_MERGE(jobs)") }
end
```

Optimizer Hints is supported not only for MySQL but also for most
databases (PostgreSQL on RDS, Oracle, SQL Server, etc), it is really
helpful to turn heavy queries for large scale applications.

1 files changed, 5 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
index a518b897a0..6eefda763f 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -103,6 +103,11 @@ module ActiveRecord
         mariadb? || version >= "5.7.5"
       end
 
+      # See https://dev.mysql.com/doc/refman/8.0/en/optimizer-hints.html for more details.
+      def supports_optimizer_hints?
+        !mariadb? && version >= "5.7.7"
+      end
+
       def supports_advisory_locks?
         true
       end