What is the difference between synchronous and asynchronous replication?

Question

Accepted Answer

**Synchronous** — wait for confirmation. **Asynchronous** — don't wait.

**Synchronous Replication:**
- Primary waits for replica acknowledgment.
- Strong consistency.
- Higher latency.
- Data loss prevention.

```
Synchronous:
Primary → Write → Replica → ACK → Primary confirms
(Primary waits for confirmation)
(Guaranteed no data loss)
```

**Asynchronous Replication:**
- Primary doesn't wait.
- Eventual consistency.
- Lower latency.
- Possible data loss.

```
Asynchronous:
Primary → Write → Primary confirms immediately
       → Replica (async)
   (Primary doesn't wait)
   (Possible data loss on failure)
```

**Key differences:**
- **Sync** — wait for confirmation.
- **Async** — don't wait.
- **Sync** — strong consistency.
- **Async** — eventual consistency.

Systems Analyst: What is the difference between synchronous and asynchronous replication?