apache/cassandra · warning

Unable to serialize metadata snapshot triggered by…

Error message

Unable to serialize metadata snapshot triggered by TriggerSnapshot transformation

What it means

MetadataSnapshotListener.notify tries to persist a cluster metadata snapshot via ClusterMetadataService.instance().snapshotManager().storeSnapshot(next) when a TriggerSnapshot transformation is applied. Serialization/persistence failures are caught and logged as a warning; the epoch is committed anyway, so only snapshot capture is lost.

Solutions

1. Check the logged Throwable stack for the root cause (IOException vs serialization class error).
2. Verify disk space and write permissions on the CMS snapshot directory.
3. If a new metadata type fails to serialize, ensure all nodes run compatible versions and the type has a registered serialization codec.
4. Retry snapshot capture manually (or via another TriggerSnapshot) once the root cause is fixed.

// Ensure snapshot dir is writable before triggering
File dir = DatabaseDescriptor.getSnapshotDirectory();
if (!dir.canWrite()) throw new IllegalStateException("Snapshot dir not writable: " + dir);

try {
    ClusterMetadataService.instance().snapshotManager().storeSnapshot(next);
} catch (IOException | SerializationException e) {
    logger.warn("Snapshot capture failed; will retry on next trigger", e);
}

When it happens

Trigger: A TriggerSnapshot transformation is committed on the CMS and storeSnapshot throws while serializing the ClusterMetadata (e.g. a transformation result that cannot be serialized, disk I/O failure on the snapshot directory, or internal serialization bug in a newly added metadata type).

Common situations: Upgrades introducing new metadata fields not serializable by older snapshot code; disk full or permissions on the snapshots directory; test environments (forceSnapshotTriggersSnapshot) where listeners run against partially constructed metadata.

Understand the failure class

Background: json.Marshal / "failed to marshal" errors in Go: why "unsupported type" happens and how to fix it — this error's family across 22 libraries.

Related errors

• Unable to parse creation time from
• Unsupported metadata version
• Addresses differ: !=
• Attempted to encode a response with an unset stream id:
• Bad CMS state:

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/64febc65ed3edaa2. Report an issue: GitHub.

Appendix: source

Thrown at src/java/org/apache/cassandra/tcm/listeners/MetadataSnapshotListener.java:52

public class MetadataSnapshotListener implements LogListener
{
    private static final Logger logger = LoggerFactory.getLogger(MetadataSnapshotListener.class);

    private static final EnumSet<Transformation.Kind> triggers = EnumSet.of(TRIGGER_SNAPSHOT, FORCE_SNAPSHOT);

    @Override
    public void notify(Entry entry, Transformation.Result result)
    {
        ClusterMetadata next = result.success().metadata;
        if (triggers.contains(entry.transform.kind()))
        {
            try
            {
                ClusterMetadataService.instance().snapshotManager().storeSnapshot(next);
            }
            catch (Throwable e)
            {
                logger.warn("Unable to serialize metadata snapshot triggered by TriggerSnapshot transformation", e);
            }
        }
    }
}

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