presto-main/src/main/java/io/prestosql/transaction/InMemoryTransactionManager.java/InMemoryTransactionManager/getTransactionMetadata
class InMemoryTransactionManager:    private TransactionMetadata getTransactionMetadata(TransactionId transactionId)
    {
        TransactionMetadata transactionMetadata = transactions.get(transactionId);
        if (transactionMetadata == null) {
            throw new NotInTransactionException(transactionId);
        }
        return transactionMetadata;
    }