Processing or queries for Data-Only-Locked tables

On data-only-locked tables, the type and duration of locks acquired for or queries using the OR Strategy (when multiple clauses might match the same rows) depend on the isolation level.

Processing or queries at isolation Levels 1 and 2

No locks are acquired on the index pages or rows of data-only-locked tables while row IDs are being retrieved from indexes and copied to a worktable. After the worktable is sorted to remove duplicate values, the data rows are re-qualified when the row IDs are used to read data from the table. If any rows were deleted, they are not returned. If any rows were updated, they are re-qualified by applying the full set of query clauses to them. The locks are released when the row qualification completes, for isolation level 1, or at the end of the transaction, for isolation level 2.

Processing or queries at isolation Level 3

Isolation level 3 requires serializable reads. At this isolation level, or queries obtain locks on the data pages or data rows during the first phase of or processing, as the worktable is being populated. These locks are held until the transaction completes. Re-qualification of rows is not required.