A file access system for user defined functions (UDFs) can be implemented on a distributed database system. The system can store UDF signatures and interfaces (e.g., classes, sub-classes) that can be called by other users. Upon a UDF being called, one or more interface objects (e.g., InputStream) can be created and requests transferred to a execution node via a network channel. The execution node can implement multiple threads that are authorized and download file data from a staging location (e.g., internal stage, external stage) concurrently.