Storage-Side Scanning on Non-Natively Formatted Data

A storage system communicatively coupled to a DBMS performs storage-side scanning of data sources that are not stored in the native database storage format of the DBMS. Data sources for external tables are accessible in a storage system referred to herein as a distributed data access system, e.g. a Hadoop Distributed File System. To execute a query that references an external table, a DBMS first generates an execution plan. The distributed data access system supplies the DBMS with information that specifies each portion of the data source, and specifies which data node to use to access the portion. The DBMS sends a request for each portion to the respective data node, the request requesting that the data node generate rows from data in the portion. The request may specify scanning criteria, specifying one or more columns to project and/or filter on. The request may also specify code modules for the data node to execute to generate rows or records and columns.