apache/cassandra · error · IllegalArgumentException

Cannot perform any operations against virtual keyspace " +…

Error message

Cannot perform any operations against virtual keyspace " + keyspaceName

What it means

Keyspace.verifyKeyspaceIsValid(keyspaceName) rejects names registered in the VirtualKeyspaceRegistry with IllegalArgumentException 'Cannot perform any operations against virtual keyspace <name>'. Virtual keyspaces (system_views, system_virtual_schema) are in-memory, non-persisted views that cannot accept writes or DDL, so operations targeting them are refused.

Solutions

1. Skip virtual keyspaces: filter out names present in VirtualKeyspaceRegistry (system_views, system_virtual_schema) before performing operations.
2. Query the virtual tables only via SELECT (CQL queries are read-only there); never target them with writes/DDL/snapshots.
3. Use Schema.instance.getKeyspaces() excluding VirtualKeyspaceRegistry entries when enumerating keyspaces for batch operations.

Example fix

// before
Keyspace.open(ksName); // fails for system_views
// after
if (VirtualKeyspaceRegistry.instance.getKeyspaceNullable(ksName) == null)
    Keyspace.open(ksName);

if (VirtualKeyspaceRegistry.instance.getKeyspaceNullable(ksName) != null)
    throw new IllegalArgumentException(ksName + " is a virtual keyspace; read-only via CQL SELECT");

static boolean isVirtualKeyspace(String ks) {
    return VirtualKeyspaceRegistry.instance.getKeyspaceNullable(ks) != null;
}

try {
    Keyspace.getValidKeyspace(ksName);
} catch (IllegalArgumentException e) {
    if (e.getMessage().startsWith("Cannot perform any operations against virtual keyspace"))
        return; // skip virtual keyspaces in batch jobs
    throw e;
}

When it happens

Trigger: Calling getValidKeyspace/verifyKeyspaceIsValid with 'system_views' or another virtual keyspace before operations like writes, schema changes, or snapshots; tooling that enumerates all keyspaces (including virtual) and then performs real operations on each.

Common situations: Scripts iterating over `DESCRIBE KEYSPACES` output that includes virtual keyspaces; monitoring tooling querying virtual tables but attempting admin operations; mistakenly treating virtual keyspace tables as regular tables for backup/restore.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• 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…
• e.getMessage()
• Invalid element selection

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/d7dc07d117ba9475. Report an issue: GitHub.

Appendix: source

Thrown at src/java/org/apache/cassandra/db/Keyspace.java:230

        if (cfs == null)
            throw new IllegalArgumentException(String.format("Unknown CF %s %s", id, columnFamilyStores));
        return cfs;
    }

    public ColumnFamilyStore getIfExists(TableId id)
    {
        return columnFamilyStores.get(id);
    }

    public boolean hasColumnFamilyStore(TableId id)
    {
        return columnFamilyStores.containsKey(id);
    }

    public static void verifyKeyspaceIsValid(String keyspaceName)
    {
        if (null != VirtualKeyspaceRegistry.instance.getKeyspaceNullable(keyspaceName))
            throw new IllegalArgumentException("Cannot perform any operations against virtual keyspace " + keyspaceName);

        if (!Schema.instance.getKeyspaces().contains(keyspaceName))
            throw new IllegalArgumentException("Keyspace " + keyspaceName + " does not exist");
    }

    public static Keyspace getValidKeyspace(String keyspaceName)
    {
        verifyKeyspaceIsValid(keyspaceName);
        return Keyspace.open(keyspaceName);
    }

    /**
     * @return A list of open SSTableReaders
     */
    public List<SSTableReader> getAllSSTables(SSTableSet sstableSet)
    {
        List<SSTableReader> list = new ArrayList<>(columnFamilyStores.size());
        for (ColumnFamilyStore cfStore : columnFamilyStores.values())

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