apache/druid · error · IllegalStateException

Emit called unexpectedly before service start

Error message

Emit called unexpectedly before service start

What it means

OpentsdbEmitter.emit checks an internal 'started' flag before processing events; emitting before start() was called means the sender and converter are not yet initialized, so it fails fast with ISE rather than silently dropping metrics.

Source

Thrown at extensions-contrib/opentsdb-emitter/src/main/java/org/apache/druid/emitter/opentsdb/OpentsdbEmitter.java:69

  }

  @Override
  public void start()
  {
    synchronized (started) {
      if (!started.get()) {
        log.info("Starting Opentsdb Emitter.");
        sender.start();
        started.set(true);
      }
    }
  }

  @Override
  public void emit(Event event)
  {
    if (!started.get()) {
      throw new ISE("Emit called unexpectedly before service start");
    }
    if (event instanceof ServiceMetricEvent) {
      OpentsdbEvent opentsdbEvent = converter.convert((ServiceMetricEvent) event);
      if (opentsdbEvent != null) {
        sender.enqueue(opentsdbEvent);
      } else {
        log.debug(
            "Metric=[%s] has not been configured to be emitted to opentsdb",
            ((ServiceMetricEvent) event).getMetric()
        );
      }
    }
  }

  @Override
  public void flush()
  {
    if (started.get()) {

View on GitHub (pinned to 9b90983fd2)

Solutions

1. Ensure emitter.start() is called before any emit() (normally Druid's Emitters service lifecycle does this)
2. If wiring manually, register the emitter with the lifecycle or call start() explicitly after construction
3. Guard early metric emissions so they occur only after service start, or flush/buffer events until started

Example fix

// before
emitter.emit(event); // may run before start
// after
if (emitter.isStarted()) {
  emitter.emit(event);
}

if (!emitter.isStarted()) { throw new IllegalStateException("start the emitter before emitting events"); }

try { emitter.emit(event); } catch (IllegalStateException e) { if (e.getMessage().contains("before service start")) { emitter.start(); emitter.emit(event); } }

When it happens

Trigger: Calling emitter.emit(event) before emitter.start(), e.g. a custom emitter pipeline registering the OpentsdbEmitter but not invoking start(), or emitting from another thread racing with service startup.

Common situations: Wiring the emitter into Druid's emitter list manually without lifecycle start, unit tests invoking emit directly, or ordering bugs where metrics are emitted during module initialization.

Understand the failure class

Background: "Invalid state transition" errors: "status must be X, actually Y", "already rejected/charging/uninstalled", "cannot ... while running" — what they mean when a library rejects your call — this error's family across 31 libraries.

Related errors

• Failed to parse metrics and dimensions
• Failed to parse metric configuration
• Service is closed.
• Already started
• can't stop.

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/b0c22e72e18d2766. Report an issue: GitHub.