presto-main/src/main/java/io/prestosql/metadata/MetadataManager.java/MetadataManager/schemaExists
class MetadataManager:    @Override
    public boolean schemaExists(Session session, CatalogSchemaName schema)
    {
        Optional<CatalogMetadata> catalog = getOptionalCatalogMetadata(session, schema.getCatalogName());
        if (!catalog.isPresent()) {
            return false;
        }
        CatalogMetadata catalogMetadata = catalog.get();
        ConnectorSession connectorSession = session.toConnectorSession(catalogMetadata.getCatalogName());
        return catalogMetadata.listConnectorIds().stream()
                .map(catalogMetadata::getMetadataFor)
                .anyMatch(metadata -> metadata.schemaExists(connectorSession, schema.getSchemaName()));
    }