Replication Types and Node Outages

Now that we have a basic understanding of replication, let’s discuss replication mechanisms and outages.

Just like in the previous lessons, let’s assume that the My Cool App has a good amount of data, but all the data can be hosted on a single machine. Now we want to build replication mechanisms so that the database system can scale and can handle more load.

Synchronous or asynchronous replication?

When a leader receives some data to write, should the replication happen synchronously or asynchronously?

Note: In synchronous replication, a write is successful only when all the followers have successfully processed the write-request. In asynchronous replication, a write is successful as soon as the leader has processed the write-request, after which the followers can process it asynchronously.

Synchronous replication guarantees that every follower in the system contains the same up-to-date data as the leader. If the leader fails, data is already available to the followers—so no write is lost.

In the above diagram, we see a visualization of synchronous replication. Upon receiving a write-request, a leader processes it in itself, then triggers the same to the followers. To report whether the write was successful, the leader waits for both followers to report that ...