Which statement best describes the execution behavior of a job updating a table when using primary key constraints in Delta Lake?

The statement that a batch job will update only modified rows in the table is accurate in the context of Delta Lake's execution behavior when primary key constraints are employed. Delta Lake efficiently manages data through its ability to perform operations like update, merge, and insert, particularly with the presence of primary keys, which ensure that data integrity is maintained.

When updating a table with primary key constraints, Delta Lake can identify which specific rows have changed and perform targeted updates. This granularity means that instead of replacing the entire table or running unnecessary operations on unchanged data, the system focuses solely on those rows that require modification. As a result, the performance of the job improves, and resource utilization is optimized since only the relevant changes are written to the underlying data storage.

In contrast, replacing the entire contents of the table is less efficient and does not leverage the advantages offered by primary keys. Incremental jobs that track changes might suggest a more complex mechanism of managing state, while dual writes would introduce additional overhead and complexity without addressing the core need of efficient updates. Thus, the execution behavior for jobs designed to update a table with primary key constraints is best represented by the notion of targeting and updating only modified rows.