apache/cassandra · error · RuntimeException

Unknown metric

Error message

Unknown metric 

What it means

This generic metric lookup (the mymetricname special-case handler) only recognizes a fixed set of metric names; anything else reaches the fallback throw new RuntimeException("Unknown metric " + metricName). It signals the caller asked for a metric this accessor does not support.

Solutions

1. Use one of the explicitly supported metric names for this method.
2. Call the type-specific accessor (getStorageMetric, getCompactionMetric, getTableMetric) that matches the metric's type instead.
3. Extend the method's switch to map the desired metric and rebuild the tools jar.
4. Inspect the JMX tree directly (e.g. via jconsole) to confirm the metric exists, then choose the right accessor.

Example fix

// before
probe.getMetric("SomeUnmappedMetric"); // unknown
// after
probe.getStorageMetric("SomeUnmappedMetric"); // use the matching accessor

if (!SUPPORTED_METRICS.contains(metricName))
    throw new IllegalArgumentException("Metric not supported by this accessor: " + metricName);

try {
    return probe.getMetric(metricName);
} catch (RuntimeException e) {
    if (String.valueOf(e.getMessage()).startsWith("Unknown metric"))
        throw new IllegalArgumentException("Unsupported metric " + metricName + "; use a type-specific accessor", e);
    throw e;
}

When it happens

Trigger: Calling the generic per-type metric getter with a name not handled by any of its branches — the name may exist in JMX but is not mapped by this NodeProbe method.

Common situations: Users assuming the method is a generic pass-through to any Cassandra metric; metric renamed between versions; copying examples for a different accessor (table vs storage vs generic).

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

Related errors

• Unknown client metric
• Unknown compaction metric
• appendAll() can only be called on non-frozen collections
• Can not initialize cluster with empty cluster identifier
• Can't abort bootstrap for - it does not exist in cluster…

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/516b45418ef2bd59. Report an issue: GitHub.

Appendix: source

Thrown at src/java/org/apache/cassandra/tools/NodeProbe.java:2346

                        new ObjectName("org.apache.cassandra.metrics:type=CIDRGroupsMappingCache,name=" + metricName),
                        CassandraMetricsRegistry.JmxCounterMBean.class).getCount();
                case CIDRAuthorizerMetrics.CIDR_GROUPS_CACHE_RELOAD_LATENCY:
                case CIDRAuthorizerMetrics.LOOKUP_CIDR_GROUPS_FOR_IP_LATENCY:
                    return JMX.newMBeanProxy(
                        mbeanServerConn,
                        new ObjectName("org.apache.cassandra.metrics:type=CIDRGroupsMappingCache,name=" + metricName),
                        CassandraMetricsRegistry.JmxTimerMBean.class).getMean();
                default:
                    if (metricName.contains(CIDRAuthorizerMetrics.CIDR_ACCESSES_REJECTED_COUNT_PREFIX) ||
                        metricName.contains(CIDRAuthorizerMetrics.CIDR_ACCESSES_ACCEPTED_COUNT_PREFIX))
                    {
                        return JMX.newMBeanProxy(
                            mbeanServerConn,
                            new ObjectName("org.apache.cassandra.metrics:type=mymetricname,name=" + metricName),
                            CassandraMetricsRegistry.JmxCounterMBean.class).getCount();
                    }

                    throw new RuntimeException("Unknown metric " + metricName);
            }
        }
        catch (MalformedObjectNameException e)
        {
            throw new RuntimeException(e);
        }
    }

    public Map<String, Long> getCountsMetricsFromVtable()
    {
        return cfmProxy.getCountsMetricsFromVtable();
    }

    public Map<String, List<Double>> getLatenciesMetricsFromVtable()
    {
        return cfmProxy.getLatenciesMetricsFromVtable();
    }

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