Directory-Based Sharding

Directory-based sharding utilizes a lookup table that keeps track of which shard holds what data. In other words, it specifies a one-to-one mapping of the data with the shard that it is stored in.

Consider the example below. A column from the original table is selected as shard key (just as we did for key-based sharding). Each shard key is then given a specific shard ID, which tells which shard has the data with its corresponding shard key. In this way, the rows of all the rows in the original table are divided into different shards.

Let's see if you understand sharding!