A file access system for user defined functions (UDFs) can be implemented on a distributed database system. The system can store UDF interfaces and file reference objects that can be called by other users. Upon a UDF being called, files on a stage, one or more interface objects (e.g., InputStream), and file reference objects can be implemented by execution nodes of the distributed database system. The execution nodes can implement multiple threads that are authenticated and can download file data from a staging location concurrently.