pin_connection!

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 336
      def pin_connection!(lock_thread) # :nodoc:
        @pinned_connection ||= (connection_lease&.connection || checkout)
        @pinned_connections_depth += 1

        # Any leased connection must be in @connections otherwise
        # some methods like #connected? won't behave correctly
        unless @connections.include?(@pinned_connection)
          @connections << @pinned_connection
        end

        @pinned_connection.lock_thread = ActiveSupport::IsolatedExecutionState.context if lock_thread
        @pinned_connection.pinned = true
        @pinned_connection.verify! # eagerly validate the connection
        @pinned_connection.begin_transaction joinable: false, _lazy: false
      end