04 Try it yourself Interactive

Change one level and watch the others hold

The same RESULT table as section 02, and the same storage change, run two ways. With mappings swaps the heap file for a B+ tree file organisation, which really does move the records, walks the change up through both mappings, and then does it again one level higher by adding a column. No mappings deletes the DBMS from the picture: a program that holds the byte offsets itself makes the identical storage change and breaks. Watch app lines to edit in each run. Nothing plays on its own: Next, Back and Reset, or the arrow keys.

With mappings
heap file · no index
Indigo = the level or mapping this step is about. Amber = changed on purpose. Green = survived untouched. Rose = broken, or missing entirely.
Press Next to begin. Each press advances the run by one step.


      

        
Change made at–

        
Mappings rewritten0

        
Correct rows out4

        
App lines to edit0

      


      

      

        
        
        
        step 0 / 0