presto-main/src/main/java/io/prestosql/metadata/MetadataManager.java/MetadataManager/beginQuery
class MetadataManager:    @Override
    public void beginQuery(Session session, Multimap<CatalogName, ConnectorTableHandle> tableHandles)
    {
        for (Entry<CatalogName, Collection<ConnectorTableHandle>> entry : tableHandles.asMap().entrySet()) {
            ConnectorMetadata metadata = getMetadata(session, entry.getKey());
            ConnectorSession connectorSession = session.toConnectorSession(entry.getKey());
            metadata.beginQuery(connectorSession, entry.getValue());
            registerCatalogForQueryId(session.getQueryId(), metadata);
        }
    }