apache/cassandra · warning · IllegalArgumentException

Unknown keyspace

Error message

Unknown keyspace %s

What it means

ColumnIndexesSystemView.data() iterates user keyspaces from Schema metadata and then fetches the live Keyspace instance. If a keyspace exists in metadata but has no live instance (dropped concurrently), getKeyspaceInstance returns null and data() throws IllegalArgumentException("Unknown keyspace ..."). This is a race between schema iteration and keyspace teardown.

Solutions

1. Retry the virtual-table query after the DROP completes
2. Avoid querying system_views.column_indexes concurrently with keyspace drops
3. Upgrade — newer versions skip such keyspaces instead of throwing

Example fix

null

for (int i = 0; i < 3; i++) {
    try { rs = session.execute(queryVirtualTable); break; }
    catch (IllegalArgumentException e) {
        if (e.getMessage().startsWith("Unknown keyspace")) { sleep(backoff); continue; }
        throw e;
    }
}

When it happens

Trigger: Querying the column_indexes virtual table while a keyspace is being dropped concurrently — Schema.instance.getUserKeyspaces() lists the keyspace, but its instance is gone by the time getKeyspaceInstance runs.

Common situations: Monitoring dashboards polling virtual tables during DROP KEYSPACE; test suites dropping schemas while another client reads virtual tables.

Understand the failure class

Background: 'Could not be found', 'does not exist', 'not found in database': the resource-not-found family when an ID, slug, key, or URI lookup comes back empty — this error's family across 20 libraries.

Related errors

• Unknown keyspace . This can occur if the keyspace is being…
• Unknown keyspace . This can occur if the keyspace is being…
• Cannot create more than one storage-attached index on the…
• Cannot instantiate a non-virtual table
• Keyspace does not exist

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/2b87d9dd3ad84dd7. Report an issue: GitHub.

Appendix: source

Thrown at src/java/org/apache/cassandra/index/sai/virtual/ColumnIndexesSystemView.java:85

                           .build());
    }

    @Override
    public void apply(PartitionUpdate update)
    {
        throw new InvalidRequestException("Modification is not supported by table " + metadata);
    }

    @Override
    public DataSet data()
    {
        SimpleDataSet dataset = new SimpleDataSet(metadata());

        for (KeyspaceMetadata ks: Schema.instance.getUserKeyspaces())
        {
            Keyspace keyspace = Schema.instance.getKeyspaceInstance(ks.name);
            if (keyspace == null)
                throw new IllegalArgumentException("Unknown keyspace " + ks.name);

            for (ColumnFamilyStore cfs : keyspace.getColumnFamilyStores())
            {
                SecondaryIndexManager manager = cfs.indexManager;
                StorageAttachedIndexGroup group = StorageAttachedIndexGroup.getIndexGroup(cfs);

                if (group != null)
                {
                    group.getIndexes().forEach(i -> {
                        StorageAttachedIndex index = (StorageAttachedIndex) i;
                        String indexName = index.identifier().indexName;

                        dataset.row(ks.name, indexName)
                               .column(TABLE_NAME, cfs.name)
                               .column(COLUMN_NAME, index.termType().columnName())
                               .column(IS_QUERYABLE, manager.isIndexQueryable(index))
                               .column(IS_BUILDING, manager.isIndexBuilding(indexName))
                               .column(IS_STRING, index.termType().isLiteral())

View on GitHub (pinned to 88fd0f6a0e)