Building software

Database Partitioning is when you split the data inside the database into smaller "databases". One partition holds a part of your data. All partitions together form the entire database.

Partitioning is often used with replication, which means each partition's data is copied onto multiple nodes. This way, even though each record is in only one partition, it can be stored on different nodes for fault tolerance. A node may hold more than one partition.

When using a leader-follower replication model, the mix of partitioning and replication might look like this:

The formula in Fig 5 is one of the reasons why Elasticsearch does not allow the update of the number of primary shards post index creation. What the default routing guarantees is that the data will be uniformly distributed across the cluster which would reduce query hotspots when retrieving documents