Figure 7-6 shows a hash-based index scan. Hash-based index scans can be performed using nonclustered indexes or clustered indexes on data-only-locked tables. Each worker process navigates higher levels of the index and reads the leaf-level pages of the index. Each worker process then hashes on either the data page ID or the key value to determine which data pages or data rows to process. Reading every leaf page produces negligible overhead.
Figure 7-6: Hash-based, nonclustered index scan
