apache/cassandra · error · CoordinatorBehindException

Coordinator schema for %s.%s with epoch %s is behind our sch

Error message

Coordinator schema for %s.%s with epoch %s is behind our schema %s

What it means

ReadCommandVerbHandler.checkSchemaVersion rejects a read request when the replica's local schema epoch is AHEAD of the epoch the coordinator serialized the command at. The replica cannot serve data under the coordinator's older schema view, so it marks coordinatorBehindSchema and throws CoordinatorBehindException, expecting the coordinator to refresh its schema.

Source

Thrown at src/java/org/apache/cassandra/db/ReadCommandVerbHandler.java:157

    {
        ReadCommand readCommand = message.payload;

        if (SchemaConstants.isSystemKeyspace(readCommand.metadata().keyspace) ||
            readCommand.serializedAtEpoch() == null) // don't try to catch up with pre-5.0 nodes
            return metadata;

        Keyspace ks = metadata.schema.getKeyspace(readCommand.metadata().keyspace);
        ColumnFamilyStore cfs = ks != null ? ks.getColumnFamilyStore(readCommand.metadata().id) : null;
        Epoch localComparisonEpoch = metadata.epoch;
        if (cfs != null)
            localComparisonEpoch = cfs.metadata().epoch;

        if (localComparisonEpoch.isBefore(readCommand.serializedAtEpoch()))
            metadata = ClusterMetadataService.instance().fetchLogFromPeerOrCMS(metadata, message.from(), message.epoch());
        else if (localComparisonEpoch.isAfter(readCommand.serializedAtEpoch()))
        {
            TCMMetrics.instance.coordinatorBehindSchema.mark();
            throw new CoordinatorBehindException(String.format("Coordinator schema for %s.%s with epoch %s is behind our schema %s",
                                                               message.payload.metadata().keyspace,
                                                               message.payload.metadata().name,
                                                               readCommand.serializedAtEpoch(),
                                                               localComparisonEpoch));
        }
        ks = metadata.schema.getKeyspace(readCommand.metadata().keyspace);
        if (ks == null || ks.getColumnFamilyStore(readCommand.metadata().id) == null)
            throw new IllegalStateException("Unknown table " + readCommand.metadata().id +" after fetching remote log entries");
        return metadata;
    }

    private ClusterMetadata checkTokenOwnership(ClusterMetadata metadata, Message<ReadCommand> message)
    {
        ReadCommand command = message.payload;

        if (command.metadata().isVirtual())
            return metadata;

View on GitHub (pinned to 88fd0f6a0e)

Solutions

Allow the coordinator to catch up on schema epochs (it should refetch the log and retry); verify with `nodetool describecluster` schema versions
On the coordinator, force a metadata log refresh/restart if it stays pinned at an old epoch
Check replica-to-CMS connectivity so epoch dissemination works
Ensure consistent Cassandra versions across the cluster during upgrades

Defensive patterns

Strategy: retry

Try / catch

try {
    result = session.execute(query);
} catch (CoordinatorBehindException e) {
    // coordinator schema older than replica; refresh session/schema metadata and retry
    cluster.refreshSchema();
    result = session.execute(query);
}

Prevention

Wait for `nodetool describecluster` to show a single schema version after DDL before issuing reads
Avoid DDL storms immediately before read-heavy workloads
Keep TCM log dissemination healthy (CMS reachability)
Restart coordinators stuck at old epochs promptly

When it happens

Trigger: A replica calls doVerb -> checkSchemaVersion; localComparisonEpoch.isAfter(readCommand.serializedAtEpoch()) and fetching the coordinator's log state from peer/CMS does not bring the coordinator up to the local epoch.

Common situations: Schema change (CREATE/ALTER TABLE) just committed and replicated, but the coordinator node has not yet applied the new epoch; coordinator behind on TCM log replay after a restart; mixing node versions during upgrade.

Understand the failure class

Background: Schema validation failed / invalid input schema: payload rejected because its shape doesn't match the expected schema — this error's family across 28 libraries.

Related errors

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/40750cf9ad8a840b. Report an issue: GitHub.