+ # 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_resolver_context` class is used by the middleware to set
+ # timestamps for the last write to the primary. The resolver uses the context
+ # 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_resolver_context = ActiveRecord::Middleware::DatabaseSelector::Resolver::Session
+