Explain difference between scaling horizontally and vertically for databases

• Horizontal scaling means that you scale by adding more machines into your pool of resources whereas
• Vertical scaling means that you scale by adding more power (CPU, RAM) to an existing machine.

In a database world horizontal-scaling is often based on the partitioning of the data i.e. each node contains only part of the data, in vertical-scaling the data resides on a single node and scaling is done through multi-core i.e. spreading the load between the CPU and RAM resources of that machine.

Good examples of horizontal scaling are Cassandra, MongoDB, Google Cloud Spanner. and a good example of vertical scaling is MySQL – Amazon RDS (The cloud version of MySQL).