nathanmarz/storm · error · RuntimeException

Non-system tuples should never be sent to __system bolt.

Error message

Non-system tuples should never be sent to __system bolt.

What it means

SystemBolt.execute is unconditional: it never processes tuples and throws immediately for any input. The __system bolt exists only to schedule builtin metrics tasks (via prepare), so receiving a tuple means something upstream is emitting to or anchoring toward the __system stream/component, which is never valid.

Solutions

1. Find the upstream component emitting to __system and remove that emission (grep for "__system" in topology code and stream declarations).
2. Rename any custom output stream that collides with the reserved __system stream name.
3. Remove any grouping/anchoring that targets the __system component; it must not receive user tuples.
4. If caused by a library, check its version/issue tracker — user code should never route tuples to the system bolt.

Example fix

// before
OutputCollector.emit("__system", tuple, values); // sends tuple to system bolt
// after
OutputCollector.emit(DEFAULT_STREAM_ID, tuple, values); // emit on your own stream

// Never emit or group to reserved system streams/components
if ("__system".equals(streamId) || "__system".equals(componentId)) {
    throw new IllegalArgumentException("__system is reserved; user code must not send tuples to it");
}

When it happens

Trigger: Any bolt or spout emits a tuple to the __system component/stream, or declares __system as an output target, delivering a tuple to SystemBolt.execute.

Common situations: Custom code accidentally names a stream '__system' or declares fields grouping/anchoring toward the system component; misconfigured builtin metrics wiring; copying Storm internals' stream names into user topology code.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• Could not instantiate a class listed in config under section
• A single worker should have 1 SystemBolt instance.
• MeanReducer::reduce called with unsupported input type
• No output fields defined for component:stream
• TopologyContext.registerMetric can only be called from…

AI-assisted analysis of nathanmarz/storm@cdb116e942 (2026-09-12). Data as JSON: /api/errors/195b09be53eacf86. Report an issue: GitHub.

Appendix: source

Thrown at storm-core/src/jvm/backtype/storm/metric/SystemBolt.java:149

        context.registerMetric("memory/heap", new MemoryUsageMetric(new AFn() {
            public Object invoke() {
                return jvmMemRT.getHeapMemoryUsage();
            }
        }), bucketSize);
        context.registerMetric("memory/nonHeap", new MemoryUsageMetric(new AFn() {
            public Object invoke() {
                return jvmMemRT.getNonHeapMemoryUsage();
            }
        }), bucketSize);

        for(GarbageCollectorMXBean b : ManagementFactory.getGarbageCollectorMXBeans()) {
            context.registerMetric("GC/" + b.getName().replaceAll("\\W", ""), new GarbageCollectorMetric(b), bucketSize);
        }
    }

    @Override
    public void execute(Tuple input) {
        throw new RuntimeException("Non-system tuples should never be sent to __system bolt.");
    }

    @Override
    public void cleanup() {
    }
}

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