presto-raptor-legacy/src/main/java/io/prestosql/plugin/raptor/legacy/RaptorConnector.java/RaptorConnector/getMetadata
class RaptorConnector:    @Override
    public ConnectorMetadata getMetadata(ConnectorTransactionHandle transaction)
    {
        RaptorMetadata metadata = transactions.get(transaction);
        checkArgument(metadata != null, "no such transaction: %s", transaction);
        return metadata;
    }