Durability
- If the DBMS tells the outside world a transaction committed, those changes must survive a crash and be visible on restart (
1:02:22,1:02:53). - Stricter levels exist: surviving a machine fire or a data-center burning down requires backups on other machines / other data centers (
1:02:53). - The mechanisms are logging and shadow paging; making them fast is a dedicated lecture on write-ahead logging, checkpoints, and recovery in a few weeks (
1:03:18).
Which mechanism delivers which ACID property
| Property | Mechanism (1:03:30, 1:03:47) |
|---|---|
| Atomicity + Durability | Redo/undo mechanisms — the write-ahead log gives both redo and undo; shadow paging gives undo |
| Consistency | Integrity constraints, plus consensus protocols (Paxos, Raft) in the distributed case |
| Isolation | Concurrency control protocols — two-phase locking, OCC (starting next week) |