What is the difference between write-ahead logging and write-behind caching?

Question

Accepted Answer

**WAL** — log before write. **Write-Behind** — write to cache, sync later.

**Write-Ahead Logging (WAL):**
- Log changes before applying.
- Recovery guarantee.
- Database transactions.
- Durability.

```
WAL:
1. Write to log file
2. Apply changes to database
3. If crash → replay log
(Log first, then apply)
```

**Write-Behind Caching:**
- Write to cache first.
- Async sync to database.
- Performance optimization.
- Possible data loss.

```
Write-Behind:
1. Write to cache (fast)
2. Async write to DB
3. If crash → possible data loss
(Cache first, sync later)
```

**Key differences:**
- **WAL** — log before write.
- **Write-Behind** — cache first.
- **WAL** — durability.
- **Write-Behind** — performance.

Systems Analyst: What is the difference between write-ahead logging and write-behind caching?