Why the log was enough

A fee collection database loses power. When it comes back the log shows:

14:00 CHECKPOINT { active: none } 14:05 T1 START 14:07 T1 UPDATE fees.paid 1200 -> 1500 14:11 T1 COMMIT 14:15 T2 START 14:18 T2 UPDATE fees.paid 1500 -> 1800 14:20 T3 START 14:24 T3 UPDATE seats.free 40 -> 39 14:29 T3 COMMIT 14:32 (power lost)

The log is on disk and complete up to 14:32. The data pages may or may not have been written; the buffer manager was free to write them at any time.

T2 never committed.