You define a custom business transaction using appd.startTransaction() and end().

If the custom transaction runs for a long time or if it crosses an asynchronous boundary, you can use resume() to rejoin the running transaction.

A downstream transaction in a distributed transaction cannot start until its upstream transaction has made its exit call.

The order of transactions respects the nonlinear nature of Node.js applications. An upstream transaction might end immediately after its exit call completes or sometime later. It is not necessary for an upstream transaction to end before or after its downstream transaction starts or ends. It is possible for a downstream transaction to end before its upstream transactions have ended.