Merge pull request #35073 from eileencodes/db-selection

Part 8: Multi db improvements, Adds basic automatic database switching to Rails

1 files changed, 20 insertions, 0 deletions

diff --git a/railties/lib/rails/generators/rails/app/templates/config/environments/production.rb.tt b/railties/lib/rails/generators/rails/app/templates/config/environments/production.rb.tt
index 08befd9196..94f7dd0c79 100644
--- a/railties/lib/rails/generators/rails/app/templates/config/environments/production.rb.tt
+++ b/railties/lib/rails/generators/rails/app/templates/config/environments/production.rb.tt
@@ -98,4 +98,24 @@ Rails.application.configure do
   # Do not dump schema after migrations.
   config.active_record.dump_schema_after_migration = false
   <%- end -%>
+
+  # Inserts middleware to perform automatic connection switching.
+  # The `database_selector` hash is used to pass options to the DatabaseSelector
+  # middleware. The `delay` is used to determine how long to wait after a write
+  # to send a subsequent read to the primary.
+  #
+  # The `database_resolver` class is used by the middleware to determine which
+  # database is appropriate to use based on the time delay.
+  #
+  # The `database_operations` class is used by the middleware to set timestamps
+  # for the last write to the primary. The resolver uses the operations class
+  # timestamps to determine how long to wait before reading from the replica.
+  #
+  # By default Rails will store a last write timestamp in the session. The
+  # DatabaseSelector middleware is designed as such you can define your own
+  # strategy for connection switching and pass that into the middleware through
+  # these configuration options.
+  # config.active_record.database_selector = { delay: 2.seconds }
+  # config.active_record.database_resolver = ActiveRecord::Middleware::DatabaseSelector::Resolver
+  # config.active_record.database_operations = ActiveRecord::Middleware::DatabaseSelector::Resolver::Session
 end