04 Try it yourself Interactive
The same two transactions from section 02, run twice. S1 is the schedule you already traced. S2 is S1 with operations 6 and 7 swapped, so T2 reads B before T1 writes it, and nothing else is different. Press Next to run one operation. After each one you get the value on disk in both rows and the precedence graph as it stands: the emerald counter is edges running T1 to T2, the rose counter is edges running the other way, and the schedule is rejected the moment both are above zero. Nothing plays on its own. Next, Back and Reset, or the arrow keys.