newrelic.setTransactionName issues

[rcoup]

I'm having problems setting a transaction name. Super-simplistically:

var app = express();
app.get('/some/path', function(req, res) {
  newrelic.setTransactionName("foo");  // this works
  console.log("PointA", newrelic.agent.tracer.getTransaction()); // shows something

  doStuff(function(err, data) {
    newrelic.setTransactionName("bar");  // "No transaction found when setting name to ..."
    console.log("PointB", newrelic.agent.tracer.getTransaction()); // undefined
    res.send(200, "something"); 
    // the "Dumped transaction state." NR log message happens here
    console.log("PointC", newrelic.agent.tracer.getTransaction()); // undefined
  });
});

Obviously doStuff() here is super-complex and involves caches and native modules and other nastiness. I can't reproduce the problem using a simplified example like the above.

If I keep a reference to the transaction object at PointA, txn.isActive() is true at PointB (even though getTransaction() still returns undefined). Similarly at PointC, getTransaction() returns undefined, but txn.isActive() is now false.

I've made sure sure require('newrelic') is the first thing done in the app. NewRelic is v1.8.1, express is v3.1.0

Any ideas or further things to investigate? Thanks :)

[wraithan]

Howdy @rcoup we don't do support via our issues anymore. We prefer if you go through https://support.newrelic.com/

Since you went a bit deeper on this than the average, I can give a quick reason why this is happening. Under the hood we use continuation-local-storage and async-listener to pass state despite how the call stack gets sliced when you hit something async. async-listener can handle the mundane cases (setTimeout, etc) and our instrumentation handles more of the advanced cases (redis, mysql, mongo, etc) for things we specifically instrument. But because of those more interesting cases, the state that cls and async-listener are passing around for you gets lost.

Once we have custom instrumentation you'll be able to account for those more interesting cases yourself, until then, without digging in and touching internals, you can't work around them.

[rcoup]

hurm. okay :)

Is it (relatively) safe enough to just do txn.partialName = "Custom/" + myName at the appropriate point? Seems like it works (and afaict only getTransaction() is confused in the above)?

[groundwater]

Using a private API is fine, but at the risk that it may break between minor version updates.

The getTransaction method has to guess for lack of a better word which transaction your callbacks belong to because the original call stack is long gone. If you explicitly hold a reference to your transaction, it will always point to the transaction in play when the variable was defined. If you declare your variable at the start of web request, it should give you what you're looking for.

The piece of the API you're touching haven't changed much, so it's probably safe if you'er in a hurry. Otherwise you may want to wait until custom instrumentation, which we'd be happy to have you help us beta test.

[rcoup]

Thanks, it'll keep me going for now. Happy to be involved with betas, ping me when you're ready.