Write-Ahead Log (WAL)
Durability and crash recovery in databases
Write-Ahead Log (Disk)
WAL is empty - run demo to see entries
Data Pages (Buffer Pool)
balance:A
$1000
LSN: 0
balance:B
$500
LSN: 0
balance:C
$750
LSN: 0
Active Transactions
No transactions
Log Entry Types
BEGIN
WRITE
COMMIT
ABORT
CHECKPOINT
Activity
Run demo to see activity
How WAL Works:
- Write-Ahead: Log changes BEFORE modifying data pages
- Checkpoint: Flush dirty pages to disk, mark recovery point
- REDO: Replay committed transactions after crash
- UNDO: Rollback uncommitted transactions
- Ensures ACID durability even after crashes