apache/cassandra · error · RuntimeException

Unknown Cache metric name

Error message

Unknown Cache metric name 

What it means

NodeProbe.getCacheMetric(String cacheType, String metricName) throws when the metricName argument is not one of the supported cache metric keys handled in the switch (e.g. Entries, Hits, Misses, Capacity, Size, HitRate, MissLatency, MissLatencyUnit). The metric name is a CLI-supplied string mapped to JMX MBean attributes, and unknown names cannot be resolved to an MBean proxy.

Source

Thrown at src/java/org/apache/cassandra/tools/NodeProbe.java:1905

                    return JMX.newMBeanProxy(mbeanServerConn,
                            new ObjectName("org.apache.cassandra.metrics:type=Cache,scope=" + cacheType + ",name=" + metricName),
                            CassandraMetricsRegistry.JmxGaugeMBean.class).getValue();
                case "Requests":
                case "Hits":
                case "Misses":
                    return JMX.newMBeanProxy(mbeanServerConn,
                            new ObjectName("org.apache.cassandra.metrics:type=Cache,scope=" + cacheType + ",name=" + metricName),
                            CassandraMetricsRegistry.JmxMeterMBean.class).getCount();
                case "MissLatency":
                    return JMX.newMBeanProxy(mbeanServerConn,
                            new ObjectName("org.apache.cassandra.metrics:type=Cache,scope=" + cacheType + ",name=" + metricName),
                            CassandraMetricsRegistry.JmxTimerMBean.class).getMean();
                case "MissLatencyUnit":
                    return JMX.newMBeanProxy(mbeanServerConn,
                            new ObjectName("org.apache.cassandra.metrics:type=Cache,scope=" + cacheType + ",name=MissLatency"),
                            CassandraMetricsRegistry.JmxTimerMBean.class).getDurationUnit();
                default:
                    throw new RuntimeException("Unknown Cache metric name " + metricName);

            }
        }
        catch (MalformedObjectNameException e)
        {
            throw new RuntimeException(e);
        }
    }

    /**
     * Retrieve buffer pool metrics based on the buffer pool type
     * @param poolType networking chunk-cache
     * @param metricName UsedSize Size
     * @return
     */
    public Object getBufferPoolMetric(String poolType, String metricName)
    {
        try

View on GitHub (pinned to 88fd0f6a0e)

Solutions

1. Use a supported metric name exactly as spelled in the switch: e.g. Entries, Hits, Misses, Capacity, Size, HitRate, MissLatency, MissLatencyUnit
2. Check `nodetool help cachemetrics` for accepted names on your version
3. Inspect available Cache MBeans via JMX (org.apache.cassandra.metrics:type=Cache) to see valid attributes

Example fix

// before
Object v = probe.getCacheMetric("KeyCache", "hitrate");
// after
Object v = probe.getCacheMetric("KeyCache", "HitRate");

java.util.Set<String> VALID = Set.of("Entries","Size","Capacity","Hits","Misses","HitRate","MissLatency","MissLatencyUnit");
if (!VALID.contains(metricName)) throw new IllegalArgumentException("Unknown cache metric: " + metricName);

try { return probe.getCacheMetric(cacheType, metricName); } catch (RuntimeException e) { throw new IllegalArgumentException("Supported cache metrics: Entries, Size, Capacity, Hits, Misses, HitRate, MissLatency, MissLatencyUnit", e); }

When it happens

Trigger: Running `nodetool cachemetrics <cacheType> <badMetricName>` with a name outside the switch cases.

Common situations: Typo or case mismatch (e.g. 'hitrate' vs 'HitRate'); expecting metrics from other tool versions; guessing metric names instead of consulting `nodetool help cachemetrics`.

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 BufferPool metric name
• Error while refreshing system.size_estimates
• Timeout type requires one of (read, range, write, counterwri
• timeout must be non-negative
• Error setting log for on level . Please check logback confi

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/04cd9292923ba86d. Report an issue: GitHub.