apache/cassandra · error · RuntimeException

Unknown compaction metric

Error message

Unknown compaction metric 

What it means

getCompactionMetric uses a switch over metricName; any name outside the supported set (CompactionCompleted, TotalCompactionsCompleted, PendingCompactions, etc.) hits the default branch and throws RuntimeException("Unknown compaction metric " + metricName). It is a fail-fast guard against unsupported metric names.

Solutions

1. Use one of the supported compaction metric names exactly as spelled in NodeProbe's switch (case-sensitive).
2. Check the NodeProbe source for your Cassandra version to enumerate valid names.
3. Add the case to NodeProbe and rebuild if you need a metric that is legitimately present in JMX but not exposed here.
4. Wrap the call in try-catch to convert the failure into a clear config error in your tooling.

Example fix

// before
probe.getCompactionMetric("CompactionsCompleted"); // unknown
// after
probe.getCompactionMetric("TotalCompactionsCompleted");

Set<String> VALID = Set.of("PendingCompactions", "CompletedCompactions", "CompactionsAborted", "CompactionsReduced", "TotalCompactionsCompleted");
if (!VALID.contains(metricName)) throw new IllegalArgumentException("Unknown compaction metric: " + metricName);

try {
    return probe.getCompactionMetric(metricName);
} catch (RuntimeException e) {
    if (String.valueOf(e.getMessage()).startsWith("Unknown compaction metric"))
        throw new IllegalArgumentException(e.getMessage() + " — valid: PendingCompactions, CompletedCompactions, TotalCompactionsCompleted, ...", e);
    throw e;
}

When it happens

Trigger: Calling getCompactionMetric(metricName) with a string not matched by any case label — e.g. a misspelled name or a metric that exists in a different Cassandra version but not this one.

Common situations: Monitoring configs written for a different Cassandra release; typos like 'totalCompactionsCompleted' (wrong case); renaming of compaction metrics between major versions.

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 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/b4a9f08c1796be97. Report an issue: GitHub.

Appendix: source

Thrown at src/java/org/apache/cassandra/tools/NodeProbe.java:2278

                case "CompressedBytesCompacted":
                case "CompactionsAborted":
                case "CompactionsReduced":
                case "SSTablesDroppedFromCompaction":
                    return JMX.newMBeanProxy(mbeanServerConn,
                            new ObjectName("org.apache.cassandra.metrics:type=Compaction,name=" + metricName),
                            CassandraMetricsRegistry.JmxCounterMBean.class);
                case "CompletedTasks":
                case "PendingTasks":
                case "PendingTasksByTableName":
                    return JMX.newMBeanProxy(mbeanServerConn,
                            new ObjectName("org.apache.cassandra.metrics:type=Compaction,name=" + metricName),
                            CassandraMetricsRegistry.JmxGaugeMBean.class).getValue();
                case "TotalCompactionsCompleted":
                    return JMX.newMBeanProxy(mbeanServerConn,
                            new ObjectName("org.apache.cassandra.metrics:type=Compaction,name=" + metricName),
                            CassandraMetricsRegistry.JmxMeterMBean.class);
                default:
                    throw new RuntimeException("Unknown compaction metric " + metricName);
            }
        }
        catch (MalformedObjectNameException e)
        {
            throw new RuntimeException(e);
        }
    }

    /**
     * Retrieve Proxy metrics
     * @param metricName
     */
    public Object getClientMetric(String metricName)
    {
        try
        {
            switch(metricName)
            {

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