Clustered indexes on data-only-locked tables are structured like nonclustered indexes. They have a leaf level above the data pages. The leaf level contains the key values and row ID for each row in the table.
Unlike clustered indexes on allpages-locked tables, the data rows in a data-only-locked table are not necessarily maintained in exact order by the key. Instead, the index directs the placement of rows to pages that have adjacent or nearby keys.
When a row needs to be inserted in a data-only-locked table with a clustered index, the insert uses the clustered index key just before the value to be inserted. The index pointers are used to find that page, and the row is inserted on the page if there is room. If there is not room, the row is inserted on a page in the same allocation unit, or on another allocation unit already used by the table.
To provide nearby space for maintaining data clustering during inserts and updates to data-only-locked tables, you can set space management properties to provide space on pages (using fillfactor and exp_row_size) or on allocation units (using reservepagegap).
See Chapter 14, “Setting Space Management Properties.”