Systems / Service evolution
Three chapters of a service
Upgrade a working reservation service without losing the orders already inside it.
Upgrade one occupied service through three chapters. Every chapter carries the real earlier reservations forward. Keep historical receipts intact.
Chapter 1: reserve Fern’s 2 units. Chapter 2: migrate each unit into 3 quanta. Chapter 3: prove recovery before and after a durable commit decision.
1 · Reserve2 · Migrate3 · Recover
Chapter 1 controls
Explore the controls, then check your result.
Need a hint?
A prepared post-image is only a proposal. Before the decision, recovery discards it. After the decision, recovery must install it exactly once—even if it was already applied before the crash.
Carried-forward storage
ServiceONLINE
Layout / indexrows / resource
Free capacity3 / 6
Occupied units3 / 6
| Customer | Allocation | Original receipt |
|---|---|---|
| Rose | 2 | Reserved 2 |
| Moss | 1 | Reserved 1 |
Resource index → shared pool: Rose, Moss
DURABLE JOURNALEmptyNo pending transaction
- Two existing customers occupy 3 of 6 units.