High-level Design for Better Availability and Scalability

Let’s see Megastore’s high-level design before discussing how Megastore improves availability and scalability.

High-level design

The components involved in the high-level design of our system are as follows:

• Application server: It is used to deploy Megastore along with the Megastore library. There is a defined local replica on each application server. By sending transactions directly to the local Bigtable, the Megastore library makes Paxos operations on that replica persistent.
• Megastore library: Applications connect to the Megastore library, which implements Paxos and other algorithms, like picking a replica for reading, catching up with a replica that is falling behind, and so on.
• Replication server: Periodically, replication servers look for unfinished writes and provide Paxos no-opno-op means no operation. It is a machine language command that does nothing. (Source: Wikipedia) values to finish them.
• Coordinator: A coordinator server keeps track of a set of entity groups for which its replica has seen every Paxos write.
• Bigtable: For scalable fault-tolerant storage within a particular data center, we utilize Google’s Bigtable, which allows us to handle arbitrary read and write throughput by distributing operations across several rows.

The following illustration shows the high-level design of Megastore components within a data center.