presto-main/src/main/java/io/prestosql/transaction/InMemoryTransactionManager.java/TransactionMetadata/createConnectorTransactionMetadata
class TransactionMetadata:        public synchronized ConnectorTransactionMetadata createConnectorTransactionMetadata(CatalogName catalogName, Catalog catalog)
        {
            Connector connector = catalog.getConnector(catalogName);
            ConnectorTransactionMetadata transactionMetadata = new ConnectorTransactionMetadata(catalogName, connector, beginTransaction(connector));
            checkState(connectorIdToMetadata.put(catalogName, transactionMetadata) == null);
            return transactionMetadata;
        }