What causes "Truncate is not supported by table " in apache/cassandra?

Remove the TRUNCATE statement; virtual table contents cannot and need not be cleared.

apache/cassandra · error · InvalidRequestException

Truncate is not supported by table

Error message

Truncate is not supported by table

What it means

CollectionVirtualTableAdapter.truncate rejects TRUNCATE statements against virtual tables. Virtual tables hold ephemeral runtime data derived from the node, so truncation is meaningless and unsupported; the framework throws InvalidRequestException unconditionally.

Source

Thrown at src/java/org/apache/cassandra/db/virtual/CollectionVirtualTableAdapter.java:585

        return (T) type.compose(value);
    }

    @Override
    public TableMetadata metadata()
    {
        return metadata;
    }

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

    @Override
    public void truncate()
    {
        throw new InvalidRequestException("Truncate is not supported by table " + metadata);
    }
}

View on GitHub (pinned to 88fd0f6a0e)

Solutions

Remove the TRUNCATE statement; virtual table contents cannot and need not be cleared.
If state needs resetting, restart the node or change the underlying runtime setting the table mirrors.
Verify the target keyspace is not a virtual keyspace (system_views, system_settings, etc.) before running maintenance scripts.

Example fix

// before
TRUNCATE system_views.threads;
// after
SELECT * FROM system_views.threads;  // read-only; no truncation possible

Defensive patterns

Strategy: validation

Validate before calling

// skip TRUNCATE for virtual tables
List<Row> virtual = session.execute("SELECT keyspace_name, table_name FROM system_schema.virtual_tables").all();
Set<String> vt = virtual.stream().map(r -> r.getString("keyspace_name")+"."+r.getString("table_name")).collect(Collectors.toSet());
if (vt.contains(ks + "." + table)) return; // do not truncate

Try / catch

try { session.execute("TRUNCATE " + ks + "." + table); }
catch (com.datastax.oss.driver.api.core.servererrors.InvalidQueryException e) {
    if (e.getMessage().contains("Truncate is not supported")) { /* ignore: virtual table */ }
    else throw e;
}

Prevention

Filter virtual keyspaces out of cleanup/truncate scripts.
Never blanket-truncate system* keyspaces.
Remember virtual table data is ephemeral node state; truncation is never needed.

When it happens

Trigger: Running `TRUNCATE <virtual_keyspace>.<virtual_table>;` (or a DROP-style data-clearing call) on any virtual table, e.g. system_views or system_settings tables.

Common situations: Cleanup scripts that blanket-truncate tables in system keyspaces; test fixtures resetting 'system' tables; misunderstanding that virtual tables persist data.

Related errors

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/4986aba7373647c3. Report an issue: GitHub.